Index: binaries/data/mods/_test.gui/gui/event/event.js
===================================================================
--- binaries/data/mods/_test.gui/gui/event/event.js
+++ binaries/data/mods/_test.gui/gui/event/event.js
@@ -13,3 +13,8 @@
 	Engine.GetGUIObjectByName("obj4").onTick = () => { ++called4; };
 };
 obj3.onTick = () => { ++called3; };
+
+function init()
+{
+	return new Promise(() => {});
+}
Index: binaries/data/mods/_test.gui/gui/hotkey/hotkey.js
===================================================================
--- binaries/data/mods/_test.gui/gui/hotkey/hotkey.js
+++ binaries/data/mods/_test.gui/gui/hotkey/hotkey.js
@@ -12,3 +12,8 @@
 		state_after = Engine.HotkeyIsPressed("test");
 	return false;
 }
+
+function init()
+{
+	return new Promise(() => {});
+}
Index: binaries/data/mods/_test.gui/gui/regainFocus/emptyPage.js
===================================================================
--- /dev/null
+++ binaries/data/mods/_test.gui/gui/regainFocus/emptyPage.js
@@ -0,0 +1,4 @@
+function init()
+{
+	return new Promise(resolve => global.closePage = resolve);
+}
Index: binaries/data/mods/_test.gui/gui/regainFocus/emptyPage.xml
===================================================================
--- /dev/null
+++ binaries/data/mods/_test.gui/gui/regainFocus/emptyPage.xml
@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<objects>
+	<script file="gui/regainFocus/emptyPage.js"/>
+</objects>
Index: binaries/data/mods/_test.gui/gui/regainFocus/page_emptyPage.xml
===================================================================
--- binaries/data/mods/_test.gui/gui/regainFocus/page_emptyPage.xml
+++ binaries/data/mods/_test.gui/gui/regainFocus/page_emptyPage.xml
@@ -1,4 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <page>
 	<include>common/styles.xml</include>
+	<include>regainFocus/emptyPage.xml</include>
 </page>
Index: binaries/data/mods/_test.gui/gui/regainFocus/pushWithPopOnInit.js
===================================================================
--- binaries/data/mods/_test.gui/gui/regainFocus/pushWithPopOnInit.js
+++ binaries/data/mods/_test.gui/gui/regainFocus/pushWithPopOnInit.js
@@ -1 +1,4 @@
-Engine.PushGuiPage("regainFocus/page_emptyPage.xml").then(Engine.PopGuiPage);
+function init()
+{
+	return Engine.PushGuiPage("regainFocus/page_emptyPage.xml");
+}
Index: binaries/data/mods/_test.gui/gui/resolveReject/page_resolveReject.xml
===================================================================
--- /dev/null
+++ binaries/data/mods/_test.gui/gui/resolveReject/page_resolveReject.xml
@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<page>
+	<include>common/styles.xml</include>
+	<include>resolveReject/resolveReject.xml</include>
+</page>
Index: binaries/data/mods/_test.gui/gui/resolveReject/resolveReject.js
===================================================================
--- /dev/null
+++ binaries/data/mods/_test.gui/gui/resolveReject/resolveReject.js
@@ -0,0 +1,5 @@
+async function init(reject)
+{
+	if (reject)
+		throw undefined;
+}
Index: binaries/data/mods/_test.gui/gui/resolveReject/resolveReject.xml
===================================================================
--- /dev/null
+++ binaries/data/mods/_test.gui/gui/resolveReject/resolveReject.xml
@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<objects>
+	<script file="gui/resolveReject/resolveReject.js"/>
+</objects>
Index: binaries/data/mods/_test.gui/gui/sequential/page_sequential.xml
===================================================================
--- /dev/null
+++ binaries/data/mods/_test.gui/gui/sequential/page_sequential.xml
@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<page>
+	<include>common/styles.xml</include>
+	<include>sequential/sequential.xml</include>
+</page>
Index: binaries/data/mods/_test.gui/gui/sequential/sequential.js
===================================================================
--- /dev/null
+++ binaries/data/mods/_test.gui/gui/sequential/sequential.js
@@ -0,0 +1,5 @@
+async function init()
+{
+	await Engine.PushGuiPage("regainFocus/page_emptyPage.xml");
+	await Engine.PushGuiPage("regainFocus/page_emptyPage.xml");
+}
Index: binaries/data/mods/_test.gui/gui/sequential/sequential.xml
===================================================================
--- /dev/null
+++ binaries/data/mods/_test.gui/gui/sequential/sequential.xml
@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<objects>
+	<script file="gui/sequential/sequential.js"/>
+</objects>
Index: binaries/data/mods/mod/gui/colormixer/colormixer.js
===================================================================
--- binaries/data/mods/mod/gui/colormixer/colormixer.js
+++ binaries/data/mods/mod/gui/colormixer/colormixer.js
@@ -1,96 +1,79 @@
+const colorMixer = {};
+
+colorMixer.width = 500;
+colorMixer.height = 400;
+colorMixer.labels = [translate("Red"), translate("Green"), translate("Blue")];
+colorMixer.captions = [translate("Cancel"), translate("Save")];
+
 /**
- * @class ColorMixer
+ * ColorMixer
  * This class allows to mix color using sliders one for each of three channels in range of 0 to 255 with step of 1, returning sanitized color when closing
  */
-class ColorMixer
+function init(originalColor)
 {
-	/**
-	 * @param {String} color - initial color as RGB string e.g. 100 0 200
-	 */
-	constructor(color)
-	{
-		this.panel = Engine.GetGUIObjectByName("main");
-		this.colorDisplay = Engine.GetGUIObjectByName("colorDisplay");
+	const colorDisplay = Engine.GetGUIObjectByName("colorDisplay");
 
-		this.color = [0, 0, 0];
-		this.sliders = [];
-		this.valuesText = [];
+	const color = [0, 0, 0];
+	const sliders = [];
+	const valuesText = [];
 
-		this.setup(color);
-	}
+	Engine.GetGUIObjectByName("titleBar").caption = translate("Color");
+	Engine.GetGUIObjectByName("infoLabel").caption = translate("Move the sliders to change the Red, Green and Blue components of the Color");
 
-	setup(color)
-	{
-		Engine.GetGUIObjectByName("titleBar").caption = translate("Color");
-		Engine.GetGUIObjectByName("infoLabel").caption = translate("Move the sliders to change the Red, Green and Blue components of the Color");
-
-		const cancelHotkey = Engine.GetGUIObjectByName("cancelHotkey");
-
-		const lRDiff = this.width / 2;
-		const uDDiff = this.height / 2;
-		this.panel.size = "50%-" + lRDiff + " 50%-" + uDDiff + " 50%+" + lRDiff + " 50%+" + uDDiff;
-
-		const button = [];
-		setButtonCaptionsAndVisibitily(button, this.captions, cancelHotkey, "cmButton");
-		distributeButtonsHorizontally(button, this.captions);
-
-		const c = color.split(" ");
-
-		const object0 = Engine.GetGUIObjectByName("color[0]");
-		const height0 = object0.size.bottom - object0.size.top;
-		for (let i = 0; i < this.color.length; i++)
-		{
-			this.color[i] = Math.floor(+c[i] || 0);
-			const object = Engine.GetGUIObjectByName("color[" + i + "]");
-			if (!object)
-				continue;
-
-			const size = object.size;
-			size.top = i * height0;
-			size.bottom = size.top + height0;
-			object.size = size;
-
-			this.sliders[i] = Engine.GetGUIObjectByName("colorSlider[" + i + "]");
-			const slider = this.sliders[i];
-			slider.min_value = 0;
-			slider.max_value = 255;
-			slider.value = this.color[i];
-			slider.onValueChange = () => {this.updateFromSlider(i);};
-
-			this.valuesText[i] = Engine.GetGUIObjectByName("colorValue[" + i + "]");
-			this.valuesText[i].caption = this.color[i];
-
-			Engine.GetGUIObjectByName("colorLabel[" + i + "]").caption = this.labels[i];
-		}
-
-		this.updateColorPreview();
-		// Update return color on cancel to prevent malformed values from initial input.
-		color = this.color.join(" ");
-
-		cancelHotkey.onPress = () => { Engine.PopGuiPage(color); };
-		button[0].onPress = () => { Engine.PopGuiPage(color); };
-		button[1].onPress = () => { Engine.PopGuiPage(this.color.join(" ")); };
-	}
+	const cancelHotkey = Engine.GetGUIObjectByName("cancelHotkey");
 
-	updateFromSlider(index)
-	{
-		this.color[index] = Math.floor(this.sliders[index].value);
-		this.valuesText[index].caption = this.color[index];
-		this.updateColorPreview();
-	}
+	const lRDiff = colorMixer.width / 2;
+	const uDDiff = colorMixer.height / 2;
+	Engine.GetGUIObjectByName("main").size = "50%-" + lRDiff + " 50%-" + uDDiff + " 50%+" + lRDiff + " 50%+" + uDDiff;
+
+	const button = [];
+	setButtonCaptionsAndVisibitily(button, colorMixer.captions, cancelHotkey, "cmButton");
+	distributeButtonsHorizontally(button, colorMixer.captions);
+
+	const c = originalColor.split(" ");
 
-	updateColorPreview()
+	const updateColorPreview = () => {
+		colorDisplay.sprite = "color:" + color.join(" ");
+	};
+
+	const object0 = Engine.GetGUIObjectByName("color[0]");
+	const height0 = object0.size.bottom - object0.size.top;
+	for (let i = 0; i < color.length; i++)
 	{
-		this.colorDisplay.sprite = "color:" + this.color.join(" ");
+		color[i] = Math.floor(+c[i] || 0);
+		const object = Engine.GetGUIObjectByName("color[" + i + "]");
+		if (!object)
+			continue;
+
+		const size = object.size;
+		size.top = i * height0;
+		size.bottom = size.top + height0;
+		object.size = size;
+
+		sliders[i] = Engine.GetGUIObjectByName("colorSlider[" + i + "]");
+		const slider = sliders[i];
+		slider.min_value = 0;
+		slider.max_value = 255;
+		slider.value = color[i];
+		slider.onValueChange = () => {
+			color[i] = Math.floor(sliders[i].value);
+			valuesText[i].caption = color[i];
+			updateColorPreview();
+		};
+
+		valuesText[i] = Engine.GetGUIObjectByName("colorValue[" + i + "]");
+		valuesText[i].caption = color[i];
+
+		Engine.GetGUIObjectByName("colorLabel[" + i + "]").caption = colorMixer.labels[i];
 	}
-}
 
-ColorMixer.prototype.width = 500;
-ColorMixer.prototype.height = 400;
-ColorMixer.prototype.labels = [translate("Red"), translate("Green"), translate("Blue")];
-ColorMixer.prototype.captions = [translate("Cancel"), translate("Save")];
+	updateColorPreview();
+	// Update return color on cancel to prevent malformed values from initial input.
+	originalColor = color.join(" ");
 
-function init(color)
-{
-	new ColorMixer(color);
+	return new Promise(resolve => {
+		cancelHotkey.onPress = resolve.bind(null, originalColor);
+		button[0].onPress = resolve.bind(null, originalColor);
+		button[1].onPress = () => { resolve(color.join(" ")); };
+	});
 }
Index: binaries/data/mods/mod/gui/common/functions_msgbox.js
===================================================================
--- binaries/data/mods/mod/gui/common/functions_msgbox.js
+++ binaries/data/mods/mod/gui/common/functions_msgbox.js
@@ -1,7 +1,6 @@
-async function messageBox(mbWidth, mbHeight, mbMessage, mbTitle, mbButtonCaptions, mbBtnCode,
-	mbCallbackArgs)
+function messageBox(mbWidth, mbHeight, mbMessage, mbTitle, mbButtonCaptions)
 {
-	const btnCode = await Engine.PushGuiPage(
+	return Engine.PushGuiPage(
 		"page_msgbox.xml",
 		{
 			"width": mbWidth,
@@ -10,15 +9,11 @@
 			"title": mbTitle,
 			"buttonCaptions": mbButtonCaptions
 		});
-
-	if (mbBtnCode !== undefined && mbBtnCode[btnCode])
-		mbBtnCode[btnCode](mbCallbackArgs ? mbCallbackArgs[btnCode] : undefined);
 }
 
-async function timedConfirmation(width, height, message, timeParameter, timeout, title, buttonCaptions,
-	btnCode, callbackArgs)
+function timedConfirmation(width, height, message, timeParameter, timeout, title, buttonCaptions)
 {
-	const button = await Engine.PushGuiPage(
+	return Engine.PushGuiPage(
 		"page_timedconfirmation.xml",
 		{
 			"width": width,
@@ -29,9 +24,6 @@
 			"title": title,
 			"buttonCaptions": buttonCaptions
 		});
-
-	if (btnCode !== undefined && btnCode[button])
-		btnCode[button](callbackArgs ? callbackArgs[button] : undefined);
 }
 
 function openURL(url)
Index: binaries/data/mods/mod/gui/common/utilities.js
===================================================================
--- binaries/data/mods/mod/gui/common/utilities.js
+++ binaries/data/mods/mod/gui/common/utilities.js
@@ -21,15 +21,13 @@
 
 function setButtonCaptionsAndVisibitily(button, captions, cancelHotkey, name)
 {
-	captions.forEach((caption, i) => {
-		button[i] = Engine.GetGUIObjectByName(name + (i + 1));
-		button[i].caption = caption;
-		button[i].hidden = false;
-		button[i].onPress = () => {
-			Engine.PopGuiPage(i);
-		};
-
-		if (i == 0)
-			cancelHotkey.onPress = button[i].onPress;
+	return new Promise(resolve => {
+		captions.forEach((caption, i) => {
+			button[i] = Engine.GetGUIObjectByName(name + (i + 1));
+			button[i].caption = caption;
+			button[i].hidden = false;
+			button[i].onPress = resolve.bind(null, i);
+		});
+		cancelHotkey.onPress = resolve.bind(null, 0);
 	});
 }
Index: binaries/data/mods/mod/gui/incompatible_mods/incompatible_mods.js
===================================================================
--- binaries/data/mods/mod/gui/incompatible_mods/incompatible_mods.js
+++ binaries/data/mods/mod/gui/incompatible_mods/incompatible_mods.js
@@ -3,9 +3,5 @@
 function init(data)
 {
 	Engine.GetGUIObjectByName("mainText").caption = Engine.TranslateLines(Engine.ReadFile(g_IncompatibleModsFile));
-}
-
-function closePage()
-{
-	Engine.PopGuiPage();
+	return new Promise(resolve => Engine.GetGUIObjectByName("btnClose").onPress = resolve);
 }
Index: binaries/data/mods/mod/gui/incompatible_mods/incompatible_mods.xml
===================================================================
--- binaries/data/mods/mod/gui/incompatible_mods/incompatible_mods.xml
+++ binaries/data/mods/mod/gui/incompatible_mods/incompatible_mods.xml
@@ -17,7 +17,6 @@
 
 		<object name="btnClose" type="button" style="ModernButtonRed" size="18 100%-45 100%-18 100%-17" hotkey="cancel">
 			<translatableAttribute id="caption">Ok</translatableAttribute>
-			<action on="Press">closePage();</action>
 		</object>
 
 	</object>
Index: binaries/data/mods/mod/gui/modio/modio.js
===================================================================
--- binaries/data/mods/mod/gui/modio/modio.js
+++ binaries/data/mods/mod/gui/modio/modio.js
@@ -23,128 +23,144 @@
 
 var g_RequestStartTime;
 
-/**
- * Returns true if ModIoAdvanceRequest should be called.
- */
-var g_ModIOState = {
-	/**
-	 * Finished status indicators
-	 */
-	"ready": progressData => {
-		// GameID acquired, ready to fetch mod list
-		if (!g_RequestCancelled)
-			updateModList();
-		return true;
-	},
-	"listed": progressData => {
-		// List of available mods acquired
-
-		// Only run this once (for each update).
-		if (Engine.GetGUIObjectByName("modsAvailableList").list.length)
-			return true;
-
-		hideDialog();
-		Engine.GetGUIObjectByName("refreshButton").enabled = true;
-		g_ModsAvailableOnline = Engine.ModIoGetMods();
-		displayMods();
-		return true;
-	},
-	"success": progressData => {
-		// Successfully acquired a mod file
-		hideDialog();
-		Engine.GetGUIObjectByName("downloadButton").enabled = true;
-		return true;
-	},
-	/**
-	 * In-progress status indicators.
-	 */
-	"gameid": progressData => {
-		// Acquiring GameID from mod.io
-		return true;
-	},
-	"listing": progressData => {
-		// Acquiring list of available mods from mod.io
-		return true;
-	},
-	"downloading": progressData => {
-		// Downloading a mod file
-		updateProgressBar(progressData.progress, g_ModsAvailableOnline[selectedModIndex()].filesize);
-		return true;
-	},
-	/**
-	 * Error/Failure status indicators.
-	 */
-	"failed_gameid": progressData => {
-		// Game ID couldn't be retrieved
-		showErrorMessageBox(
-			sprintf(translateWithContext("mod.io error message", "Game ID could not be retrieved.\n\n%(technicalDetails)s"), {
-				"technicalDetails": progressData.error
-			}),
-			translateWithContext("mod.io error message", "Initialization Error"),
-			[translate("Abort"), translate("Retry")],
-			[closePage, init]);
-		return false;
-	},
-	"failed_listing": progressData => {
-		// Mod list couldn't be retrieved
-		showErrorMessageBox(
-			sprintf(translateWithContext("mod.io error message", "Mod List could not be retrieved.\n\n%(technicalDetails)s"), {
-				"technicalDetails": progressData.error
-			}),
-			translateWithContext("mod.io error message", "Fetch Error"),
-			[translate("Abort"), translate("Retry")],
-			[cancelModListUpdate, updateModList]);
-		return false;
-	},
-	"failed_downloading": progressData => {
-		// File couldn't be retrieved
-		showErrorMessageBox(
-			sprintf(translateWithContext("mod.io error message", "File download failed.\n\n%(technicalDetails)s"), {
-				"technicalDetails": progressData.error
-			}),
-			translateWithContext("mod.io error message", "Download Error"),
-			[translate("Abort"), translate("Retry")],
-			[cancelRequest, downloadMod]);
-		return false;
-	},
-	"failed_filecheck": progressData => {
-		// The file is corrupted
-		showErrorMessageBox(
-			sprintf(translateWithContext("mod.io error message", "File verification error.\n\n%(technicalDetails)s"), {
-				"technicalDetails": progressData.error
-			}),
-			translateWithContext("mod.io error message", "Verification Error"),
-			[translate("Abort")],
-			[cancelRequest]);
-		return false;
-	},
-	/**
-	 * Default
-	 */
-	"none": progressData => {
-		// Nothing has happened yet.
-		return true;
-	}
-};
-
 function init(data)
 {
-	progressDialog(
-		translate("Initializing mod.io interface."),
-		translate("Initializing"),
-		false,
-		translate("Cancel"),
-		closePage);
-
-	g_Failure = false;
-	Engine.ModIoStartGetGameId();
+	return new Promise(resolve => {
+		/**
+		 * Returns true if ModIoAdvanceRequest should be called.
+		 */
+		var modIOState = {
+			/**
+			 * Finished status indicators
+			 */
+			"ready": progressData => {
+				// GameID acquired, ready to fetch mod list
+				if (!g_RequestCancelled)
+					updateModList(resolve);
+				return true;
+			},
+			"listed": progressData => {
+				// List of available mods acquired
+
+				// Only run this once (for each update).
+				if (Engine.GetGUIObjectByName("modsAvailableList").list.length)
+					return true;
+
+				hideDialog();
+				Engine.GetGUIObjectByName("refreshButton").enabled = true;
+				g_ModsAvailableOnline = Engine.ModIoGetMods();
+				displayMods();
+				return true;
+			},
+			"success": progressData => {
+				// Successfully acquired a mod file
+				hideDialog();
+				Engine.GetGUIObjectByName("downloadButton").enabled = true;
+				return true;
+			},
+			/**
+			 * In-progress status indicators.
+			 */
+			"gameid": progressData => {
+				// Acquiring GameID from mod.io
+				return true;
+			},
+			"listing": progressData => {
+				// Acquiring list of available mods from mod.io
+				return true;
+			},
+			"downloading": progressData => {
+				// Downloading a mod file
+				updateProgressBar(
+					progressData.progress,
+					g_ModsAvailableOnline[selectedModIndex()].filesize);
+				return true;
+			},
+			/**
+			 * Error/Failure status indicators.
+			 */
+			"failed_gameid": progressData => {
+				// Game ID couldn't be retrieved
+				showErrorMessageBox(
+					sprintf(translateWithContext(
+						"mod.io error message",
+						"Game ID could not be retrieved.\n\n%(technicalDetails)s"), {
+						"technicalDetails": progressData.error
+					}),
+					translateWithContext("mod.io error message", "Initialization Error"),
+					[translate("Abort"), translate("Retry")]).then(button => {
+						[resolve, init][button]();
+					});
+				return false;
+			},
+			"failed_listing": progressData => {
+				// Mod list couldn't be retrieved
+				showErrorMessageBox(
+					sprintf(translateWithContext(
+						"mod.io error message",
+						"Mod List could not be retrieved.\n\n%(technicalDetails)s"), {
+						"technicalDetails": progressData.error
+					}),
+					translateWithContext("mod.io error message", "Fetch Error"),
+					[translate("Abort"), translate("Retry")].then(button => {
+						[cancelModListUpdate, updateModList][button](resolve)
+					});
+				return false;
+			},
+			"failed_downloading": progressData => {
+				// File couldn't be retrieved
+				showErrorMessageBox(
+					sprintf(translateWithContext(
+						"mod.io error message",
+						"File download failed.\n\n%(technicalDetails)s"), {
+						"technicalDetails": progressData.error
+					}),
+					translateWithContext("mod.io error message", "Download Error"),
+					[translate("Abort"), translate("Retry")]).then(button => {
+						[cancelRequest, downloadMod][button]()
+					});
+				return false;
+			},
+			"failed_filecheck": progressData => {
+				// The file is corrupted
+				showErrorMessageBox(
+					sprintf(translateWithContext(
+						"mod.io error message",
+						"File verification error.\n\n%(technicalDetails)s"), {
+						"technicalDetails": progressData.error
+					}),
+					translateWithContext("mod.io error message", "Verification Error"),
+					[translate("Abort")]).then(() => cancelRequest);
+				return false;
+			},
+			/**
+			 * Default
+			 */
+			"none": progressData => {
+				// Nothing has happened yet.
+				return true;
+			}
+		};
+		Engine.GetGUIObjectByName("modio").onTick = onTick.bind(null, modIOState);
+		Engine.GetGUIObjectByName("closePageBtn").onPress = resolve;
+
+		progressDialog(
+			translate("Initializing mod.io interface."),
+			translate("Initializing"),
+			false,
+			translate("Cancel"),
+			resolve);
+
+		g_Failure = false;
+		Engine.ModIoStartGetGameId();
+	});
 }
 
-function onTick()
+function onTick(modIOState)
 {
 	let progressData = Engine.ModIoGetDownloadProgress();
 
-	let handler = g_ModIOState[progressData.status];
+	let handler = modIOState[progressData.status];
 	if (!handler)
 	{
 		warn("Unrecognized progress status: " + progressData.status);
@@ -223,13 +239,13 @@
 	Engine.GetGUIObjectByName("modError").caption = isSelected && isInvalid ? sprintf(translate("Invalid mod: %(error)s"), {"error": g_ModsAvailableOnline[selected].error }) : "";
 }
 
-function cancelModListUpdate()
+function cancelModListUpdate(resolve)
 {
 	cancelRequest();
 
 	if (!g_ModsAvailableOnline.length)
 	{
-		closePage();
+		resolve();
 		return;
 	}
 
@@ -237,7 +253,7 @@
 	Engine.GetGUIObjectByName('refreshButton').enabled = true;
 }
 
-function updateModList()
+function updateModList(resolve)
 {
 	clearModList();
 	Engine.GetGUIObjectByName("refreshButton").enabled = false;
@@ -247,7 +263,7 @@
 		translate("Updating"),
 		false,
 		translate("Cancel Update"),
-		cancelModListUpdate);
+		cancelModListUpdate.bind(null, resolve));
 
 	g_Failure = false;
 	g_RequestCancelled = false;
@@ -285,18 +301,13 @@
 	hideDialog();
 }
 
-function closePage()
-{
-	Engine.PopGuiPage();
-}
-
 function showErrorMessageBox(caption, title, buttonCaptions, buttonActions)
 {
 	if (g_Failure)
 		return;
 
-	messageBox(500, 250, caption, title, buttonCaptions, buttonActions);
 	g_Failure = true;
+	return messageBox(500, 250, caption, title, buttonCaptions, buttonActions);
 }
 
 function progressDialog(dialogCaption, dialogTitle, showProgressBar, buttonCaption, buttonAction)
Index: binaries/data/mods/mod/gui/modio/modio.xml
===================================================================
--- binaries/data/mods/mod/gui/modio/modio.xml
+++ binaries/data/mods/mod/gui/modio/modio.xml
@@ -8,11 +8,6 @@
 	<object type="image" sprite="ModernFade"/>
 
 	<object name="modio" type="image" style="ModernDialog" size="10% 10% 90% 90%">
-
-		<action on="Tick">
-			onTick();
-		</action>
-
 		<!-- Page Title -->
 		<object style="ModernLabelText" type="text" size="50%-128 -18 50%+128 14">
 			<translatableAttribute id="caption">mod.io Mods</translatableAttribute>
@@ -84,9 +79,8 @@
 		</object>
 
 		<!-- Buttons -->
-		<object type="button" style="ModernButtonRed" size="100%-552 100%-44 100%-372 100%-16">
+		<object name="closePageBtn" type="button" style="ModernButtonRed" size="100%-552 100%-44 100%-372 100%-16">
 			<translatableAttribute id="caption">Back</translatableAttribute>
-			<action on="Press">closePage();</action>
 		</object>
 
 		<object name="refreshButton" type="button" style="ModernButtonRed" size="100%-368 100%-44 100%-188 100%-16" enabled="false">
Index: binaries/data/mods/mod/gui/modmod/help/help.js
===================================================================
--- binaries/data/mods/mod/gui/modmod/help/help.js
+++ binaries/data/mods/mod/gui/modmod/help/help.js
@@ -1,4 +1,5 @@
 function init(data)
 {
 	Engine.GetGUIObjectByName("mainText").caption = Engine.TranslateLines(Engine.ReadFile("gui/modmod/help/help.txt"));
+	return new Promise(resolve => Engine.GetGUIObjectByName("closeButton").onPress = resolve)
 }
Index: binaries/data/mods/mod/gui/modmod/help/help.xml
===================================================================
--- binaries/data/mods/mod/gui/modmod/help/help.xml
+++ binaries/data/mods/mod/gui/modmod/help/help.xml
@@ -17,9 +17,8 @@
 			<object name="mainText" type="text" style="ModernTextPanel"/>
 		</object>
 
-		<object type="button" style="ModernButtonRed" tooltip_style="snToolTip" size="100%-602 100%-52 100%-412 100%-24" hotkey="cancel">
+		<object name="closeButton" type="button" style="ModernButtonRed" tooltip_style="snToolTip" size="100%-602 100%-52 100%-412 100%-24" hotkey="cancel">
 			<translatableAttribute id="caption">Close</translatableAttribute>
-			<action on="Press">Engine.PopGuiPage();</action>
 		</object>
 		<object type="button" style="ModernButtonRed" size="100%-408 100%-52 100%-218 100%-24">
 			<translatableAttribute id="caption">Modding Guide</translatableAttribute>
Index: binaries/data/mods/mod/gui/modmod/modmod.js
===================================================================
--- binaries/data/mods/mod/gui/modmod/modmod.js
+++ binaries/data/mods/mod/gui/modmod/modmod.js
@@ -85,6 +85,8 @@
 	initGUIButtons(data);
 	if (g_HasIncompatibleMods)
 		Engine.PushGuiPage("page_incompatible_mods.xml", {});
+
+	return new Promise(() => {});
 }
 
 function initMods()
Index: binaries/data/mods/mod/gui/msgbox/msgbox.js
===================================================================
--- binaries/data/mods/mod/gui/msgbox/msgbox.js
+++ binaries/data/mods/mod/gui/msgbox/msgbox.js
@@ -15,7 +15,6 @@
 
 	// Default behaviour
 	let mbCancelHotkey = Engine.GetGUIObjectByName("mbCancelHotkey");
-	mbCancelHotkey.onPress = Engine.PopGuiPage;
 
 	// Calculate size
 	let mbLRDiff = data.width / 2;
@@ -25,6 +24,8 @@
 	let captions = data.buttonCaptions || [translate("OK")];
 
 	let mbButton = [];
-	setButtonCaptionsAndVisibitily(mbButton, captions, mbCancelHotkey, "mbButton");
+	const promise = setButtonCaptionsAndVisibitily(mbButton, captions, mbCancelHotkey, "mbButton")
 	distributeButtonsHorizontally(mbButton, captions);
+
+	return promise;
 }
Index: binaries/data/mods/mod/gui/pregame/mainmenu.js
===================================================================
--- binaries/data/mods/mod/gui/pregame/mainmenu.js
+++ binaries/data/mods/mod/gui/pregame/mainmenu.js
@@ -3,4 +3,6 @@
 	Engine.SwitchGuiPage("page_modmod.xml", {
 		"cancelbutton": false
 	});
+
+	return new Promise(() => {});
 }
Index: binaries/data/mods/mod/gui/termsdialog/termsdialog.js
===================================================================
--- binaries/data/mods/mod/gui/termsdialog/termsdialog.js
+++ binaries/data/mods/mod/gui/termsdialog/termsdialog.js
@@ -20,6 +20,12 @@
 	Engine.GetGUIObjectByName("title").caption = data.title;
 	initURLButtons(data.termsURL, data.urlButtons);
 	initLanguageSelection();
+
+	return new Promise(resolve => {
+		for (const [name, accepted] of [["declineButton", false], ["connectButton", true]])
+			Engine.GetGUIObjectByName(name).onPress =
+				resolve.bind(null, { "page": g_TermsPage, "accepted": accepted });
+	});
 }
 
 function initURLButtons(termsURL, urlButtons)
@@ -82,11 +88,3 @@
 
 	languageDropdown.selected = languageDropdown.list.length - 1;
 }
-
-function closeTerms(accepted)
-{
-	Engine.PopGuiPage({
-		"page": g_TermsPage,
-		"accepted": accepted
-	});
-}
Index: binaries/data/mods/mod/gui/termsdialog/termsdialog.xml
===================================================================
--- binaries/data/mods/mod/gui/termsdialog/termsdialog.xml
+++ binaries/data/mods/mod/gui/termsdialog/termsdialog.xml
@@ -29,14 +29,12 @@
 			<object size="170 0 330 100%" type="button" name="button[1]" style="ModernButtonRed" hidden="true"/>
 
 			<object size="100%-355 0 100% 100%">
-				<object type="button" style="ModernButtonRed" size="0 0 160 100%" hotkey="cancel">
+				<object name="declineButton" type="button" style="ModernButtonRed" size="0 0 160 100%" hotkey="cancel">
 					<translatableAttribute id="caption">Decline</translatableAttribute>
-					<action on="Press">closeTerms(false);</action>
 				</object>
 
 				<object name="connectButton" type="button" style="ModernButtonRed" size="170 0 330 100%">
 					<translatableAttribute id="caption">Accept</translatableAttribute>
-					<action on="Press">closeTerms(true);</action>
 				</object>
 			</object>
 		</object>
Index: binaries/data/mods/mod/gui/timedconfirmation/timedconfirmation.js
===================================================================
--- binaries/data/mods/mod/gui/timedconfirmation/timedconfirmation.js
+++ binaries/data/mods/mod/gui/timedconfirmation/timedconfirmation.js
@@ -1,74 +1,54 @@
 /**
- * @class TimedConfirmation
- * This class displays confirmation box, which will be closed after defined time in miliseconds.
+ * TimedConfirmation
+ * This page displays confirmation box, which will be closed after defined time in miliseconds.
+ *
+ * @param {Object} data
+ * @param {Number} data.width - The width of the confirmation box
+ * @param {Number} data.height - The height of the confirmation box
+ * @param {String} data.message - The message to be displayed with parameter for time which will be displayed in seconds
+ * @param {String} data.timeParameter - The string used in 'message' for time, e.g 'time' with %(time)s in message
+ * @param {Number} data.timeout - The time in miliseconds after which confirmation box closes itself
+ * @param {String} data.title - The string displayed in header
+ * @param {String|undefined} data.buttonCaptions - The captions used for buttons (if not defined, defaults to 'OK')
+ * @param {String|undefined} data.font - The used font
  */
-class TimedConfirmation
+function init(data)
 {
-	/**
-	 * @param {Object} data
-	 * @param {Number} data.width - The width of the confirmation box
-	 * @param {Number} data.height - The height of the confirmation box
-	 * @param {String} data.message - The message to be displayed with parameter for time which will be displayed in seconds
-	 * @param {String} data.timeParameter - The string used in 'message' for time, e.g 'time' with %(time)s in message
-	 * @param {Number} data.timeout - The time in miliseconds after which confirmation box closes itself
-	 * @param {String} data.title - The string displayed in header
-	 * @param {String|undefined} data.buttonCaptions - The captions used for buttons (if not defined, defaults to 'OK')
-	 * @param {String|undefined} data.font - The used font
-	 */
-	constructor(data)
-	{
-		this.messageObject = Engine.GetGUIObjectByName("tmcText");
-		this.panel = Engine.GetGUIObjectByName("tmcMain");
-		this.panel.onTick = this.onTick.bind(this);
-		this.setup(data);
-	}
+	const messageObject = Engine.GetGUIObjectByName("tmcText");
+	const panel = Engine.GetGUIObjectByName("tmcMain");
 
-	setup(data)
+	const timeout = +data.timeout + Date.now();
+	const updateDisplayedTimer = remaining =>
 	{
-		Engine.GetGUIObjectByName("tmcTitleBar").caption = data.title;
-
-		this.timeout = +data.timeout + Date.now();
-		this.message = data.message;
-		this.timeParameter = data.timeParameter;
+		messageObject.caption = sprintf(
+			data.message,
+			{ [data.timeParameter]: Math.ceil(remaining / 1000) }
+		);
+	};
+	panel.onTick = () => {
+		const remaining = timeout - Date.now();
+		if (remaining < 1)
+			Engine.GetGUIObjectByName("tmcButton1").onPress();
+		updateDisplayedTimer(remaining);
+	};
+	Engine.GetGUIObjectByName("tmcTitleBar").caption = data.title;
 
-		if (data.font)
-			this.messageObject.font = data.font;
+	if (data.font)
+		messageObject.font = data.font;
 
-		this.updateDisplayedTimer(data.timeout);
+	updateDisplayedTimer(data.timeout);
 
-		const cancelHotkey = Engine.GetGUIObjectByName("tmcCancelHotkey");
-		cancelHotkey.onPress = Engine.PopGuiPage;
+	const cancelHotkey = Engine.GetGUIObjectByName("tmcCancelHotkey");
 
-		const lRDiff = data.width / 2;
-		const uDDiff = data.height / 2;
-		this.panel.size = "50%-" + lRDiff + " 50%-" + uDDiff + " 50%+" + lRDiff + " 50%+" + uDDiff;
+	const lRDiff = data.width / 2;
+	const uDDiff = data.height / 2;
+	panel.size = "50%-" + lRDiff + " 50%-" + uDDiff + " 50%+" + lRDiff + " 50%+" + uDDiff;
 
-		const captions = data.buttonCaptions || [translate("OK")];
+	const captions = data.buttonCaptions || [translate("OK")];
 
-		const button = [];
-		setButtonCaptionsAndVisibitily(button, captions, cancelHotkey, "tmcButton");
-		distributeButtonsHorizontally(button, captions);
-	}
+	const button = [];
+	const promise = setButtonCaptionsAndVisibitily(button, captions, cancelHotkey, "tmcButton");
+	distributeButtonsHorizontally(button, captions);
 
-	onTick()
-	{
-		const remaining = this.timeout - Date.now();
-		if (remaining < 1)
-			Engine.GetGUIObjectByName("tmcButton1").onPress();
-
-		this.updateDisplayedTimer(remaining);
-	}
-
-	updateDisplayedTimer(time)
-	{
-		this.messageObject.caption = sprintf(
-			this.message,
-			{ [this.timeParameter]: Math.ceil(time / 1000) }
-		);
-	}
-}
-
-function init(data)
-{
-	new TimedConfirmation(data);
+	return promise;
 }
Index: binaries/data/mods/public/gui/autostart/autostart.js
===================================================================
--- binaries/data/mods/public/gui/autostart/autostart.js
+++ binaries/data/mods/public/gui/autostart/autostart.js
@@ -1,4 +1,5 @@
 function init(initData)
 {
-	return new AutoStart(initData);
+	new AutoStart(initData);
+	return new Promise(() => {});
 }
Index: binaries/data/mods/public/gui/campaigns/default_menu/CampaignMenu.js
===================================================================
--- binaries/data/mods/public/gui/campaigns/default_menu/CampaignMenu.js
+++ binaries/data/mods/public/gui/campaigns/default_menu/CampaignMenu.js
@@ -246,4 +246,6 @@
 		error(sprintf(translate("Error loading campaign run %s: %s."), CampaignRun.getCurrentRunFilename(), err));
 		Engine.SwitchGuiPage("page_pregame.xml", {});
 	}
+
+	return new Promise(() => {});
 }
Index: binaries/data/mods/public/gui/campaigns/default_menu/endgame/endgame.js
===================================================================
--- binaries/data/mods/public/gui/campaigns/default_menu/endgame/endgame.js
+++ binaries/data/mods/public/gui/campaigns/default_menu/endgame/endgame.js
@@ -8,4 +8,6 @@
 	let run = CampaignRun.getCurrentRun();
 	if (endGameData.won)
 		markLevelComplete(run, endGameData.initData.levelID);
+
+	return new Promise(() => {});
 }
Index: binaries/data/mods/public/gui/campaigns/load_modal/LoadModal.js
===================================================================
--- binaries/data/mods/public/gui/campaigns/load_modal/LoadModal.js
+++ binaries/data/mods/public/gui/campaigns/load_modal/LoadModal.js
@@ -92,24 +92,24 @@
 		});
 	}
 
-	deleteSelectedRun()
+	async deleteSelectedRun()
 	{
 		if (this.selectedRun === -1)
 			return;
 
 		let run = this.currentRuns[this.selectedRun];
 
-		messageBox(
+		const button = await messageBox(
 			400, 200,
 			sprintf(translate("Are you sure you want to delete run %s? This cannot be undone."), run.getLabel()),
 			translate("Confirmation"),
-			[translate("No"), translate("Yes")],
-			[null, () => {
-				run.destroy();
-				this.currentRuns.splice(this.selectedRun, 1);
-				this.selectedRun = -1;
-			}]
-		);
+			[translate("No"), translate("Yes")];
+
+		if (button === 0)
+			return;
+		run.destroy();
+		this.currentRuns.splice(this.selectedRun, 1);
+		this.selectedRun = -1;
 	}
 
 	startSelectedRun()
@@ -139,4 +139,5 @@
 function init()
 {
 	g_LoadModal = new LoadModal();
+	return new Promise(() => {});
 }
Index: binaries/data/mods/public/gui/campaigns/new_modal/NewCampaignModal.js
===================================================================
--- binaries/data/mods/public/gui/campaigns/new_modal/NewCampaignModal.js
+++ binaries/data/mods/public/gui/campaigns/new_modal/NewCampaignModal.js
@@ -3,26 +3,13 @@
  * asking you to name it.
  * Will then create the file with the according name and start everything up.
  */
-class NewCampaignModal
+function init(campaignTemplate)
 {
-	constructor(campaignTemplate)
-	{
-		this.template = campaignTemplate;
-
-		Engine.GetGUIObjectByName('cancelButton').onPress = () => Engine.PopGuiPage();
-		Engine.GetGUIObjectByName('startButton').onPress = () => this.createAndStartCampaign();
-		Engine.GetGUIObjectByName('runDescription').caption = translateWithContext("Campaign Template", this.template.Name);
-		Engine.GetGUIObjectByName('runDescription').onTextEdit = () => {
-			Engine.GetGUIObjectByName('startButton').enabled = Engine.GetGUIObjectByName('runDescription').caption.length > 0;
-		};
-		Engine.GetGUIObjectByName('runDescription').focus();
-	}
-
-	createAndStartCampaign()
-	{
-		let filename = this.template.identifier + "_" + Date.now() + "_" + Math.floor(Math.random()*100000);
-		let run = new CampaignRun(filename)
-			.setTemplate(this.template)
+	Engine.GetGUIObjectByName('startButton').onPress = () => {
+		const filename = campaignTemplate.identifier + "_" + Date.now() + "_" +
+			Math.floor(Math.random()*100000);
+		const run = new CampaignRun(filename)
+			.setTemplate(campaignTemplate)
 			.setMeta(Engine.GetGUIObjectByName('runDescription').caption)
 			.save()
 			.setCurrent();
@@ -30,13 +17,13 @@
 		Engine.SwitchGuiPage(run.getMenuPath(), {
 			"filename": run.filename
 		});
-	}
-}
-
-
-var g_NewCampaignModal;
-
-function init(campaign_template_data)
-{
-	g_NewCampaignModal = new NewCampaignModal(campaign_template_data);
+	};
+	Engine.GetGUIObjectByName('runDescription').caption =
+		translateWithContext("Campaign Template", campaignTemplate.Name);
+	Engine.GetGUIObjectByName('runDescription').onTextEdit = () => {
+		Engine.GetGUIObjectByName('startButton').enabled =
+			Engine.GetGUIObjectByName('runDescription').caption.length > 0;
+	};
+	Engine.GetGUIObjectByName('runDescription').focus();
+	return new Promise(resolve => Engine.GetGUIObjectByName('cancelButton').onPress = resolve);
 }
Index: binaries/data/mods/public/gui/campaigns/setup/CampaignSetupPage.js
===================================================================
--- binaries/data/mods/public/gui/campaigns/setup/CampaignSetupPage.js
+++ binaries/data/mods/public/gui/campaigns/setup/CampaignSetupPage.js
@@ -68,4 +68,5 @@
 function init()
 {
 	g_CampaignSetupPage = new CampaignSetupPage();
+	return new Promise(() => {});
 }
Index: binaries/data/mods/public/gui/common/functions_utility.js
===================================================================
--- binaries/data/mods/public/gui/common/functions_utility.js
+++ binaries/data/mods/public/gui/common/functions_utility.js
@@ -296,7 +296,12 @@
 {
 	let completionValue = { "nextPage": page, "args": args };
 	while (completionValue?.nextPage != null)
+	{
+		warn(completionValue.nextPage);
 		completionValue = await Engine.PushGuiPage(completionValue.nextPage, completionValue.args);
+	}
+
+	warn(uneval(completionValue));
 
 	return completionValue;
 }
Index: binaries/data/mods/public/gui/credits/credits.js
===================================================================
--- binaries/data/mods/public/gui/credits/credits.js
+++ binaries/data/mods/public/gui/credits/credits.js
@@ -56,6 +56,8 @@
 		category => {
 			Engine.GetGUIObjectByName("creditsText").caption = g_PanelData[category].content;
 		});
+
+	return new Promise(resolve => Engine.GetGUIObjectByName("closeButton").onPress = resolve);
 }
 
 // Run through a "Content" list and parse elements for formatting and translation
Index: binaries/data/mods/public/gui/credits/credits.xml
===================================================================
--- binaries/data/mods/public/gui/credits/credits.xml
+++ binaries/data/mods/public/gui/credits/credits.xml
@@ -28,11 +28,8 @@
 		</object>
 
 		<!-- Close dialog -->
-		<object type="button" style="ModernButtonRed" size="100%-200 100%-45 100%-17 100%-17" hotkey="cancel">
+		<object name="closeButton" type="button" style="ModernButtonRed" size="100%-200 100%-45 100%-17 100%-17" hotkey="cancel">
 			<translatableAttribute id="caption">Close</translatableAttribute>
-			<action on="Press">
-				Engine.PopGuiPage();
-			</action>
 		</object>
 	</object>
 </objects>
Index: binaries/data/mods/public/gui/gamesetup/gamesetup.js
===================================================================
--- binaries/data/mods/public/gui/gamesetup/gamesetup.js
+++ binaries/data/mods/public/gui/gamesetup/gamesetup.js
@@ -40,11 +40,10 @@
  */
 var g_SetupWindow;
 
-// TODO: Remove these two global functions by specifying the JS class name in the XML of the GUI page.
-
 function init(initData, hotloadData)
 {
 	g_SetupWindow = new SetupWindow(initData, hotloadData);
+	return new Promise(() => {});
 }
 
 function getHotloadData()
Index: binaries/data/mods/public/gui/gamesetup_mp/gamesetup_mp.js
===================================================================
--- binaries/data/mods/public/gui/gamesetup_mp/gamesetup_mp.js
+++ binaries/data/mods/public/gui/gamesetup_mp/gamesetup_mp.js
@@ -28,48 +28,68 @@
 {
 	g_UserRating = attribs.rating;
 
-	switch (attribs.multiplayerGameType)
-	{
-	case "join":
-	{
-		if (!Engine.HasXmppClient())
+	return new Promise(resolve => {
+
+		switch (attribs.multiplayerGameType)
 		{
-			switchSetupPage("pageJoin");
-			break;
-		}
-		if (attribs.hasPassword)
+		case "join":
 		{
-			g_ServerName = attribs.name;
-			g_ServerId = attribs.hostJID;
-			switchSetupPage("pagePassword");
+			if (!Engine.HasXmppClient())
+			{
+				switchSetupPage("pageJoin");
+				break;
+			}
+			if (attribs.hasPassword)
+			{
+				g_ServerName = attribs.name;
+				g_ServerId = attribs.hostJID;
+				switchSetupPage("pagePassword");
+			}
+			else
+			{
+				const result = startJoinFromLobby(attribs.name, attribs.hostJID, "");
+				if (result === "switch")
+					switchSetupPage("pageConnecting");
+				else if (result === "close")
+					resolve();
+			}
+			break;
 		}
-		else if (startJoinFromLobby(attribs.name, attribs.hostJID, ""))
-			switchSetupPage("pageConnecting");
-		break;
-	}
-	case "host":
-	{
-		let hasXmppClient = Engine.HasXmppClient();
-		Engine.GetGUIObjectByName("hostSTUNWrapper").hidden = !hasXmppClient;
-		Engine.GetGUIObjectByName("hostPasswordWrapper").hidden = !hasXmppClient;
-		if (hasXmppClient)
+		case "host":
 		{
-			Engine.GetGUIObjectByName("hostPlayerName").caption = attribs.name;
-			Engine.GetGUIObjectByName("hostServerName").caption =
-				sprintf(translate("%(name)s's game"), { "name": attribs.name });
+			let hasXmppClient = Engine.HasXmppClient();
+			Engine.GetGUIObjectByName("hostSTUNWrapper").hidden = !hasXmppClient;
+			Engine.GetGUIObjectByName("hostPasswordWrapper").hidden = !hasXmppClient;
+			if (hasXmppClient)
+			{
+				Engine.GetGUIObjectByName("hostPlayerName").caption = attribs.name;
+				Engine.GetGUIObjectByName("hostServerName").caption =
+					sprintf(translate("%(name)s's game"), { "name": attribs.name });
+
+				Engine.GetGUIObjectByName("useSTUN").checked =
+					Engine.ConfigDB_GetValue("user", "lobby.stun.enabled") == "true";
+			}
 
-			Engine.GetGUIObjectByName("useSTUN").checked = Engine.ConfigDB_GetValue("user", "lobby.stun.enabled") == "true";
+			switchSetupPage("pageHost");
+			break;
+		}
+		default:
+			error("Unrecognised multiplayer game type: " + attribs.multiplayerGameType);
+			break;
 		}
 
-		switchSetupPage("pageHost");
-		break;
-	}
-	default:
-		error("Unrecognised multiplayer game type: " + attribs.multiplayerGameType);
-		break;
-	}
+		Engine.GetGUIObjectByName("cancelButton").onPress = () => cancelSetup() && resolve();
+		Engine.GetGUIObjectByName("multiplayerPages").onTick = () =>
+			g_IsConnecting && pollAndHandleNetworkClient() && resolve();
+		Engine.GetGUIObjectByName("continueButton").onPress = () => confirmSetup() && resolve();
+		Engine.GetGUIObjectByName("confirmPasswordButton").onPress = () =>
+			confirmPassword() && resolve();
+	});
 }
 
+/**
+ * return whether the page should be closed.
+ */
 function cancelSetup()
 {
 	if (g_IsConnecting)
@@ -81,8 +101,7 @@
 	// Keep the page open if an attempt to join/host by ip failed
 	if (!g_IsConnecting || (Engine.HasXmppClient() && g_GameType == "client"))
 	{
-		Engine.PopGuiPage();
-		return;
+		return true;
 	}
 
 	g_IsConnecting = false;
@@ -94,14 +113,24 @@
 		switchSetupPage("pageHost");
 	else
 		error("cancelSetup: Unrecognised multiplayer game type: " + g_GameType);
+
+	return false;
 }
 
 function confirmPassword()
 {
 	if (Engine.GetGUIObjectByName("pagePassword").hidden)
-		return;
-	if (startJoinFromLobby(g_ServerName, g_ServerId, Engine.GetGUIObjectByName("clientPassword").caption))
+		return false;
+
+	const result = startJoinFromLobby(
+		g_ServerName,
+		g_ServerId,
+		Engine.GetGUIObjectByName("clientPassword").caption);
+
+	if (result === "switch")
 		switchSetupPage("pageConnecting");
+
+	return result === "close";
 }
 
 function confirmSetup()
@@ -112,16 +141,19 @@
 		let joinServer = Engine.GetGUIObjectByName("joinServer").caption;
 		let joinPort = Engine.GetGUIObjectByName("joinPort").caption;
 
-		if (startJoin(joinPlayerName, joinServer, getValidPort(joinPort)))
+		const result = startJoin(joinPlayerName, joinServer, getValidPort(joinPort));
+		if (result === "switch")
 			switchSetupPage("pageConnecting");
+		return result === "close";
 	}
-	else if (!Engine.GetGUIObjectByName("pageHost").hidden)
+
+	if (!Engine.GetGUIObjectByName("pageHost").hidden)
 	{
 		let hostServerName = Engine.GetGUIObjectByName("hostServerName").caption;
 		if (!hostServerName)
 		{
 			Engine.GetGUIObjectByName("hostFeedback").caption = translate("Please enter a valid server name.");
-			return;
+			return false;
 		}
 
 		let hostPort = Engine.GetGUIObjectByName("hostPort").caption;
@@ -132,14 +164,19 @@
 					"min": g_ValidPorts.min,
 					"max": g_ValidPorts.max
 				});
-			return;
+			return false;
 		}
 
 		let hostPlayerName = Engine.GetGUIObjectByName("hostPlayerName").caption;
 		let hostPassword = Engine.GetGUIObjectByName("hostPassword").caption;
-		if (startHost(hostPlayerName, hostServerName, getValidPort(hostPort), hostPassword))
+
+		const result = startHost(hostPlayerName, hostServerName, getValidPort(hostPort), hostPassword)
+		if (result === "switch")
 			switchSetupPage("pageConnecting");
+		return result === "close";
 	}
+
+	return false;
 }
 
 function startConnectionStatus(type)
@@ -150,14 +187,6 @@
 	Engine.GetGUIObjectByName("connectionStatus").caption = translate("Connecting to server...");
 }
 
-function onTick()
-{
-	if (!g_IsConnecting)
-		return;
-
-	pollAndHandleNetworkClient();
-}
-
 function getConnectionFailReason(reason)
 {
 	switch (reason)
@@ -202,9 +231,9 @@
 				switch (message.status)
 				{
 				case "failed":
-					cancelSetup();
+					const shouldClose = cancelSetup();
 					reportConnectionFail(message.reason, false);
-					return;
+					return shouldClose;
 
 				default:
 					error("Unrecognised netstatus type: " + message.status);
@@ -216,9 +245,9 @@
 				switch (message.status)
 				{
 				case "disconnected":
-					cancelSetup();
+					const shouldClose = cancelSetup();
 					reportDisconnect(message.reason, false);
-					return;
+					return shouldClose;
 
 				default:
 					error("Unrecognised netstatus type: " + message.status);
@@ -238,7 +267,7 @@
 				});
 
 				// Process further pending netmessages in the session page
-				return;
+				return false;
 
 			case "chat":
 				break;
@@ -259,9 +288,9 @@
 				switch (message.status)
 				{
 				case "failed":
-					cancelSetup();
+					const shouldClose = cancelSetup();
 					reportConnectionFail(message.reason, false);
-					return;
+					return shouldClose;
 
 				default:
 					error("Unrecognised netstatus type: " + message.status);
@@ -281,18 +310,19 @@
 					{
 						Engine.GetGUIObjectByName("connectionStatus").caption = translate("Game has already started, rejoining...");
 						g_IsRejoining = true;
-						return; // we'll process the game setup messages in the next tick
+						return false; // we'll process the game setup messages in the next tick
 					}
 					Engine.SwitchGuiPage("page_gamesetup.xml", {
 						"serverName": g_ServerName,
 						"hasPassword": g_ServerHasPassword
 					});
-					return; // don't process any more messages - leave them for the game GUI loop
+					// don't process any more messages - leave them for the game GUI loop
+					return false;
 
 				case "disconnected":
-					cancelSetup();
+					const shouldClose = cancelSetup();
 					reportDisconnect(message.reason, false);
-					return;
+					return shouldClose;
 
 				default:
 					error("Unrecognised netstatus type: " + message.status);
@@ -309,6 +339,8 @@
 			}
 		}
 	}
+
+	return false;
 }
 
 function switchSetupPage(newPage)
@@ -350,16 +382,16 @@
 	Engine.ConfigDB_CreateValue("user", "playername.multiplayer", playername);
 	Engine.ConfigDB_CreateValue("user", "multiplayerhosting.port", port);
 	Engine.ConfigDB_SaveChanges("user");
-	
+
 	let hostFeedback = Engine.GetGUIObjectByName("hostFeedback");
 
 	// Disallow identically named games in the multiplayer lobby
 	if (Engine.HasXmppClient() &&
 	    Engine.GetGameList().some(game => game.name == servername))
 	{
-		cancelSetup();
+		const shouldClose = cancelSetup();
 		hostFeedback.caption = translate("Game name already in use.");
-		return false;
+		return shouldClose ? "close" : "nothing";
 	}
 
 	let useSTUN = Engine.HasXmppClient() && Engine.GetGUIObjectByName("useSTUN").checked;
@@ -370,13 +402,13 @@
 	}
 	catch (e)
 	{
-		cancelSetup();
+		const shouldClose = cancelSetup();
 		messageBox(
 			400, 200,
 			sprintf(translate("Cannot host game: %(message)s."), { "message": e.message }),
 			translate("Error")
 		);
-		return false;
+		return shouldClose ? "close" : "nothing";
 	}
 
 	g_ServerName = servername;
@@ -385,7 +417,7 @@
 	if (Engine.HasXmppClient())
 		Engine.LobbySetPlayerPresence("playing");
 
-	return true;
+	return "switch";
 }
 
 /**
@@ -399,13 +431,13 @@
 	}
 	catch (e)
 	{
-		cancelSetup();
+		const shouldClose = cancelSetup();
 		messageBox(
 			400, 200,
 			sprintf(translate("Cannot join game: %(message)s."), { "message": e.message }),
 			translate("Error")
 		);
-		return false;
+		return shouldClose ? "close" : "nothing";
 	}
 
 	startConnectionStatus("client");
@@ -419,7 +451,7 @@
 	Engine.ConfigDB_CreateValue("user", "multiplayerserver", ip);
 	Engine.ConfigDB_CreateValue("user", "multiplayerjoining.port", port);
 	Engine.ConfigDB_SaveChanges("user");
-	return true;
+	return "switch";
 }
 
 /**
@@ -429,13 +461,13 @@
 {
 	if (!Engine.HasXmppClient())
 	{
-		cancelSetup();
+		const shouldClose = cancelSetup();
 		messageBox(
 			400, 200,
 			sprintf("You cannot join a lobby game without logging in to the lobby."),
 			translate("Error")
 		);
-		return false;
+		return shouldClose ? "close" : "nothing";
 	}
 
 	try
@@ -444,20 +476,20 @@
 	}
 	catch (e)
 	{
-		cancelSetup();
+		const shouldClose = cancelSetup();
 		messageBox(
 			400, 200,
 			sprintf(translate("Cannot join game: %(message)s."), { "message": e.message }),
 			translate("Error")
 		);
-		return false;
+		return shouldClose ? "close" : "nothing";
 	}
 
 	startConnectionStatus("client");
 
 	Engine.LobbySetPlayerPresence("playing");
 
-	return true;
+	return "switch";
 }
 
 function getDefaultGameName()
Index: binaries/data/mods/public/gui/gamesetup_mp/gamesetup_mp.xml
===================================================================
--- binaries/data/mods/public/gui/gamesetup_mp/gamesetup_mp.xml
+++ binaries/data/mods/public/gui/gamesetup_mp/gamesetup_mp.xml
@@ -9,11 +9,6 @@
 	<object type="image" sprite="ModernFade"/>
 
 	<object name="multiplayerPages" type="image" style="ModernDialog" size="50%-230 50%-120 50%+230 50%+120">
-
-		<action on="Tick">
-			onTick();
-		</action>
-
 		<object style="ModernLabelText" type="text" size="50%-128 0%-16 50%+128 16">
 			<translatableAttribute id="caption">Multiplayer</translatableAttribute>
 		</object>
@@ -134,12 +129,10 @@
 
 		<object name="continueButton" hotkey="confirm" type="button" size="50%+5 100%-45 100%-18 100%-17" style="ModernButtonRed">
 			<translatableAttribute id="caption">Continue</translatableAttribute>
-			<action on="Press">confirmSetup();</action>
 		</object>
 
-		<object type="button" style="ModernButtonRed" size="18 100%-45 50%-5 100%-17" hotkey="cancel">
+		<object name="cancelButton" type="button" style="ModernButtonRed" size="18 100%-45 50%-5 100%-17" hotkey="cancel">
 			<translatableAttribute id="caption">Cancel</translatableAttribute>
-			<action on="Press">cancelSetup();</action>
 		</object>
 
 		<object name="pageConnecting" hidden="true">
@@ -160,7 +153,6 @@
 			</object>
 			<object name="confirmPasswordButton" hotkey="confirm" type="button" size="50%+5 100%-45 100%-18 100%-17" style="ModernButtonRed">
 				<translatableAttribute id="caption">Confirm</translatableAttribute>
-				<action on="Press">confirmPassword();</action>
 			</object>
 		</object>
 	</object>
Index: binaries/data/mods/public/gui/hotkeys/HotkeysPage.js
===================================================================
--- binaries/data/mods/public/gui/hotkeys/HotkeysPage.js
+++ binaries/data/mods/public/gui/hotkeys/HotkeysPage.js
@@ -23,7 +23,6 @@
 		this.saveButton = Engine.GetGUIObjectByName("hotkeySave");
 		this.saveButton.enabled = false;
 
-		Engine.GetGUIObjectByName("hotkeyClose").onPress = () => Engine.PopGuiPage();
 		Engine.GetGUIObjectByName("hotkeyReset").onPress = () => this.resetUserHotkeys();
 		this.saveButton.onPress = () => {
 			this.saveUserHotkeys();
@@ -149,27 +148,26 @@
 		this.setupHotkeyList();
 	}
 
-	resetUserHotkeys()
+	async resetUserHotkeys()
 	{
-		messageBox(
+		const button = await messageBox(
 			400, 200,
 			translate("Reset all hotkeys to default values?\nWARNING: this cannot be reversed."),
 			translate("Confirmation"),
-			[translate("No"), translate("Yes")],
-			[
-				() => {},
-				() => {
-					for (let cat in this.categories)
-						this.categories[cat].hotkeys.forEach(([name, _]) => {
-							Engine.ConfigDB_RemoveValue("user", "hotkey." + name);
-						});
-					Engine.ConfigDB_SaveChanges("user");
-					Engine.ReloadHotkeys();
-					this.saveButton.enabled = false;
-					this.setupHotkeyData();
-					this.setupHotkeyList();
-				}
-			]);
+			[translate("No"), translate("Yes")]);
+
+		if (button === 0)
+			return;
+
+		for (let cat in this.categories)
+			this.categories[cat].hotkeys.forEach(([name, _]) => {
+				Engine.ConfigDB_RemoveValue("user", "hotkey." + name);
+			});
+		Engine.ConfigDB_SaveChanges("user");
+		Engine.ReloadHotkeys();
+		this.saveButton.enabled = false;
+		this.setupHotkeyData();
+		this.setupHotkeyList();
 	}
 
 	saveUserHotkeys()
@@ -193,6 +191,7 @@
 function init()
 {
 	let hotkeyPage = new HotkeysPage(new HotkeyMetadata());
+	return new Promise(resolve => Engine.GetGUIObjectByName("hotkeyClose").onPress = resolve;
 }
 
 HotkeysPage.prototype.UnavailableTooltipString = markForTranslation("No tooltip available.");
Index: binaries/data/mods/public/gui/loadgame/SavegameDeleter.js
===================================================================
--- binaries/data/mods/public/gui/loadgame/SavegameDeleter.js
+++ binaries/data/mods/public/gui/loadgame/SavegameDeleter.js
@@ -42,22 +42,21 @@
 		return tooltip;
 	}
 
-	deleteGame(gameID, label)
+	async deleteGame(gameID, label)
 	{
-		if (Engine.HotkeyIsPressed("session.savedgames.noconfirmation"))
-			this.reallyDeleteGame(gameID);
-		else
-			messageBox(
+		if (!Engine.HotkeyIsPressed("session.savedgames.noconfirmation"))
+		{
+			const button = await messageBox(
 				500, 200,
 				sprintf(translate("\"%(label)s\""), { "label": label }) + "\n" +
 					translate("Saved game will be permanently deleted, are you sure?"),
 				translate("DELETE"),
-				[translate("No"), translate("Yes")],
-				[null, () => { this.reallyDeleteGame(gameID); }]);
-	}
+				[translate("No"), translate("Yes")]);
+
+			if (button === 0)
+				return;
+		}
 
-	reallyDeleteGame(gameID)
-	{
 		if (!Engine.DeleteSavedGame(gameID))
 			error("Could not delete saved game: " + gameID);
 
Index: binaries/data/mods/public/gui/loadgame/SavegameList.js
===================================================================
--- binaries/data/mods/public/gui/loadgame/SavegameList.js
+++ binaries/data/mods/public/gui/loadgame/SavegameList.js
@@ -40,7 +40,7 @@
 			let metadata = this.savedGamesMetadata[this.gameSelection.selected];
 			let label = this.generateSavegameLabel(metadata, engineInfo);
 			for (let handler of this.selectionChangeHandlers)
-				handler.onSelectionChange(gameId, metadata, label);
+				handler(gameId, metadata, label);
 		};
 
 		this.updateSavegameList();
Index: binaries/data/mods/public/gui/loadgame/SavegameLoader.js
===================================================================
--- binaries/data/mods/public/gui/loadgame/SavegameLoader.js
+++ binaries/data/mods/public/gui/loadgame/SavegameLoader.js
@@ -1,35 +1,30 @@
 /**
- * This class is responsible for display and performance of the Load button.
+ * This is responsible for display and performance of the Load button.
  */
-class SavegameLoader
+async function loadSavegame(list)
 {
-	constructor()
-	{
-		this.confirmButton = Engine.GetGUIObjectByName("confirmButton");
-		this.confirmButton.caption = translate("Load");
-		this.confirmButton.enabled = false;
-	}
+	Engine.GetGUIObjectByName("title").caption = translate("Load Game");
+	list.selectFirst();
+	const confirmButton = Engine.GetGUIObjectByName("confirmButton");
+	confirmButton.caption = translate("Load");
+	confirmButton.enabled = false;
 
-	onSelectionChange(gameID, metadata, label)
+	while (true)
 	{
-		this.confirmButton.enabled = !!metadata;
-		this.confirmButton.onPress = () => {
-			this.loadGame(gameID, metadata);
-		};
-	}
+		const [gameID, metadata] = await new Promise(resolve => {
+			list.registerSelectionChangeHandler((gameID, metadata) => {
+				confirmButton.enabled = !!metadata;
+				confirmButton.onPress = resolve.bind(null, [gameID, metadata]);
+			});
+		});
 
-	loadGame(gameId, metadata)
-	{
 		// Check compatibility before really loading it
 		let engineInfo = Engine.GetEngineInfo();
 		let sameMods = hasSameMods(metadata.mods, engineInfo.mods);
 		let sameEngineVersion = metadata.engine_version && metadata.engine_version == engineInfo.engine_version;
 
 		if (sameEngineVersion && sameMods)
-		{
-			Engine.PopGuiPage(gameId);
-			return;
-		}
+			return gameID
 
 		// Version not compatible ... ask for confirmation
 		let message = "";
@@ -54,11 +49,13 @@
 
 		message += translate("Do you still want to proceed?");
 
-		messageBox(
+		const button = await messageBox(
 			500, 250,
 			message,
 			translate("Warning"),
-			[translate("No"), translate("Yes")],
-			[undefined, Engine.PopGuiPage.bind(Engine, gameId)]);
+			[translate("No"), translate("Yes")]);
+
+		if (button === 1)
+			return gameID;
 	}
 }
Index: binaries/data/mods/public/gui/loadgame/SavegamePage.js
===================================================================
--- binaries/data/mods/public/gui/loadgame/SavegamePage.js
+++ binaries/data/mods/public/gui/loadgame/SavegamePage.js
@@ -1,44 +1,20 @@
 /**
- * This class is responsible for loading the affected GUI control classes,
- * and setting them up to communicate with each other.
+ * This is responsible for loading the affected GUI control classes, and setting
+ * them up to communicate with each other.
  */
-class SavegamePage
+function init(data)
 {
-	constructor(data)
-	{
-		this.savegameList = new SavegameList(data && data.campaignRun || null);
-
-		this.savegameDetails = new SavegameDetails();
-		this.savegameList.registerSelectionChangeHandler(this.savegameDetails);
+	const savegameList = new SavegameList(data && data.campaignRun || null);
 
-		this.savegameDeleter = new SavegameDeleter();
-		this.savegameDeleter.registerSavegameListChangeHandler(this.savegameList);
-		this.savegameList.registerSelectionChangeHandler(this.savegameDeleter);
+	const savegameDetails = new SavegameDetails();
+	savegameList.registerSelectionChangeHandler((...args) => savegameDetails.onSelectionChange(...args));
 
-		const savePage = !!data?.savedGameData;
-		if (savePage)
-		{
-			this.savegameWriter = new SavegameWriter(data.savedGameData);
-			this.savegameList.registerSelectionChangeHandler(this.savegameWriter);
-			let size = this.savegameList.gameSelection.size;
-			size.bottom -= 24;
-			this.savegameList.gameSelection.size = size;
-		}
-		else
-		{
-			this.savegameLoader = new SavegameLoader();
-			this.savegameList.registerSelectionChangeHandler(this.savegameLoader);
-			this.savegameList.selectFirst();
-		}
-
-		Engine.GetGUIObjectByName("title").caption = savePage ? translate("Save Game") : translate("Load Game");
-		Engine.GetGUIObjectByName("cancel").onPress = () => { Engine.PopGuiPage(); };
-	}
-}
+	const savegameDeleter = new SavegameDeleter();
+	savegameDeleter.registerSavegameListChangeHandler(savegameList);
+	savegameList.registerSelectionChangeHandler((...args) => savegameDeleter.onSelectionChange(...args));
 
-var g_SavegamePage;
-
-function init(data)
-{
-	g_SavegamePage = new SavegamePage(data);
+	return Promise.race([
+		(data?.savedGameData ? writeSavegame : loadSavegame)(savegameList, data?.savedGameData),
+		new Promise(resolve => Engine.GetGUIObjectByName("cancel").onPress = resolve)
+	]);
 }
Index: binaries/data/mods/public/gui/loadgame/SavegameWriter.js
===================================================================
--- binaries/data/mods/public/gui/loadgame/SavegameWriter.js
+++ binaries/data/mods/public/gui/loadgame/SavegameWriter.js
@@ -1,70 +1,60 @@
 /**
- * This class obtains the current simulation state to be saved along the savegame,
+ * This obtains the current simulation state to be saved along the savegame,
  * asks the user whether to overwrite a savegame and performs the saving.
  */
-class SavegameWriter
+async function writeSavegame(list, savedGameData)
 {
-	constructor(savedGameData)
 	{
-		this.savedGameData = savedGameData;
-
-		let saveNew = () => {
-			this.saveGame();
-		};
+		const size = list.gameSelection.size;
+		size.bottom -= 24;
+		list.gameSelection.size = size;
+	}
 
-		this.confirmButton = Engine.GetGUIObjectByName("confirmButton");
-		this.confirmButton.caption = translate("Save");
-		this.confirmButton.onPress = saveNew;
+	Engine.GetGUIObjectByName("title").caption = translate("Save Game");
 
-		this.saveGameDesc = Engine.GetGUIObjectByName("saveGameDesc");
-		this.saveGameDesc.hidden = false;
-		this.saveGameDesc.onPress = saveNew;
-		this.descriptionChanged = false;
-		this.saveGameDesc.onTextEdit = () => {
-			this.descriptionChanged = true;
-		};
-	}
+	const confirmButton = Engine.GetGUIObjectByName("confirmButton");
+	confirmButton.caption = translate("Save");
 
-	onSelectionChange(gameID, metadata, label)
-	{
-		if (!this.descriptionChanged && metadata && typeof metadata.description === "string")
-			this.saveGameDesc.caption = metadata.description;
-		this.confirmButton.onPress = () => {
-			this.saveGame(gameID, label);
-		};
-	}
+	const saveGameDesc = Engine.GetGUIObjectByName("saveGameDesc");
+	saveGameDesc.hidden = false;
+	let descriptionChanged = false;
+	saveGameDesc.onTextEdit = () => descriptionChanged = true;
 
-	saveGame(gameID, label)
+	const gameID = await (async() =>
 	{
-		let desc = this.saveGameDesc.caption;
-		let name = gameID || "savegame";
-
-		if (!gameID)
+		while (true)
 		{
-			this.reallySaveGame(name, desc, true);
-			return;
+			const [gameID, label] = await new Promise(resolve => {
+				const saveNew = resolve.bind(null, []);
+				saveGameDesc.onPress = saveNew;
+				confirmButton.onPress = saveNew;
+				list.registerSelectionChangeHandler((gameID, metadata, label) => {
+					if (!descriptionChanged && metadata &&
+						typeof metadata.description === "string")
+						saveGameDesc.caption = metadata.description;
+					confirmButton.onPress = resolve.bind(null, [gameID, label]);
+				});
+			});
+
+			if (!gameID)
+				return;
+
+			const button = await messageBox(
+				500, 200,
+				sprintf(translate("\"%(label)s\""), { "label": label }) + "\n" +
+					translate("Saved game will be permanently overwritten, are you sure?"),
+				translate("OVERWRITE SAVE"),
+				[translate("No"), translate("Yes")]);
+
+			if (button === 1)
+				return gameID;
 		}
+	})();
 
-		messageBox(
-			500, 200,
-			sprintf(translate("\"%(label)s\""), { "label": label }) + "\n" +
-				translate("Saved game will be permanently overwritten, are you sure?"),
-			translate("OVERWRITE SAVE"),
-			[translate("No"), translate("Yes")],
-			[null, () => { this.reallySaveGame(name, desc, false); }]);
-	}
-
-	reallySaveGame(name, desc, nameIsPrefix)
-	{
-		let simulationState = Engine.GuiInterfaceCall("GetSimulationState");
-		this.savedGameData.timeElapsed = simulationState.timeElapsed;
-		this.savedGameData.states = simulationState.players.map(pState => pState.state);
+	const simulationState = Engine.GuiInterfaceCall("GetSimulationState");
+	savedGameData.timeElapsed = simulationState.timeElapsed;
+	savedGameData.states = simulationState.players.map(pState => pState.state);
 
-		if (nameIsPrefix)
-			Engine.SaveGamePrefix(name, desc, this.savedGameData);
-		else
-			Engine.SaveGame(name, desc, this.savedGameData);
-
-		Engine.PopGuiPage();
-	}
+	const saveFunc = gameID ? Engine.SaveGame : Engine.SaveGamePrefix;
+	saveFunc(gameID || "savegame", saveGameDesc.caption, savedGameData);
 }
Index: binaries/data/mods/public/gui/loading/loading.js
===================================================================
--- binaries/data/mods/public/gui/loading/loading.js
+++ binaries/data/mods/public/gui/loading/loading.js
@@ -11,6 +11,7 @@
 	};
 
 	Engine.SetCursor("cursor-wait");
+	return new Promise(() => {});
 }
 
 /**
Index: binaries/data/mods/public/gui/lobby/LobbyHandler.js
===================================================================
--- binaries/data/mods/public/gui/lobby/LobbyHandler.js
+++ binaries/data/mods/public/gui/lobby/LobbyHandler.js
@@ -3,13 +3,18 @@
  */
 class LobbyHandler
 {
-	constructor(dialog)
+	constructor(dialog, resolve)
 	{
 		this.xmppMessages = new XmppMessages();
 
 		this.profilePage = new ProfilePage(this.xmppMessages);
 		this.leaderboardPage = new LeaderboardPage(this.xmppMessages);
-		this.lobbyPage = new LobbyPage(dialog, this.xmppMessages, this.leaderboardPage, this.profilePage);
+		this.lobbyPage = new LobbyPage(
+			dialog,
+			this.xmppMessages,
+			this.leaderboardPage,
+			this.profilePage,
+			resolve);
 
 		this.xmppMessages.processHistoricMessages();
 
Index: binaries/data/mods/public/gui/lobby/LobbyPage/Buttons/JoinButton.js
===================================================================
--- binaries/data/mods/public/gui/lobby/LobbyPage/Buttons/JoinButton.js
+++ binaries/data/mods/public/gui/lobby/LobbyPage/Buttons/JoinButton.js
@@ -27,7 +27,7 @@
 	/**
 	 * Immediately rejoin and join game setups. Otherwise confirm late-observer join attempt.
 	 */
-	onPress()
+	async onPress()
 	{
 		let game = this.gameList.selectedGame();
 		if (!game)
@@ -37,24 +37,29 @@
 		let playername = rating ? g_Nickname + " (" + rating + ")" : g_Nickname;
 
 		if (!game.isCompatible)
-			messageBox(
+		{
+			const button = await messageBox(
 				400, 200,
 				translate("Your active mods do not match the mods of this game.") + "\n\n" +
 					comparedModsString(game.mods, Engine.GetEngineInfo().mods) + "\n\n" +
 					translate("Do you want to switch to the mod selection page?"),
 				translate("Incompatible mods"),
-				[translate("No"), translate("Yes")],
-				[null, this.openModSelectionPage.bind(this)]
-			);
+				[translate("No"), translate("Yes")]);
+			if (button === 1)
+				this.openModSelectionPage()
+		}
 		else if (game.stanza.state == "init" || game.players.some(player => player.Name == playername))
 			this.joinSelectedGame();
 		else
-			messageBox(
+		{
+			const button = await messageBox(
 				400, 200,
 				translate("The game has already started. Do you want to join as observer?"),
 				translate("Confirmation"),
-				[translate("No"), translate("Yes")],
-				[null, this.joinSelectedGame.bind(this)]);
+				[translate("No"), translate("Yes")]);
+			if (button === 1)
+				this.joinSelectedGame();
+		}
 	}
 
 	/**
Index: binaries/data/mods/public/gui/lobby/LobbyPage/Buttons/QuitButton.js
===================================================================
--- binaries/data/mods/public/gui/lobby/LobbyPage/Buttons/QuitButton.js
+++ binaries/data/mods/public/gui/lobby/LobbyPage/Buttons/QuitButton.js
@@ -3,8 +3,10 @@
  */
 class QuitButton
 {
-	constructor(dialog, leaderboardPage, profilePage)
+	constructor(dialog, leaderboardPage, profilePage, resolve)
 	{
+		this.resolve = resolve;
+
 		let closeDialog = this.closeDialog.bind(this);
 		let returnToMainMenu = this.returnToMainMenu.bind(this);
 		let onPress = dialog ? closeDialog : returnToMainMenu;
@@ -29,7 +31,7 @@
 	closeDialog()
 	{
 		Engine.LobbySetPlayerPresence("playing");
-		Engine.PopGuiPage();
+		this.resolve();
 	}
 
 	returnToMainMenu()
Index: binaries/data/mods/public/gui/lobby/LobbyPage/ConnectionHandler.js
===================================================================
--- binaries/data/mods/public/gui/lobby/LobbyPage/ConnectionHandler.js
+++ binaries/data/mods/public/gui/lobby/LobbyPage/ConnectionHandler.js
@@ -45,7 +45,7 @@
 			banned ? translate("BANNED") : translate("KICKED"));
 	}
 
-	askReconnect()
+	async askReconnect()
 	{
 		if (this.kicked)
 			return;
@@ -56,19 +56,14 @@
 
 		this.askingReconnect = true;
 
-		messageBox(
+		const button = await messageBox(
 			400, 200,
 			translate("You have been disconnected from the lobby. Do you want to reconnect?"),
 			translate("Confirmation"),
-			[translate("No"), translate("Yes")],
-			[
-				() => {
-					this.askingReconnect = false;
-				},
-				() => {
-					this.askingReconnect = false;
-					Engine.ConnectXmppClient();
-				}
-			]);
+			[translate("No"), translate("Yes")]);
+
+		this.askingReconnect = false;
+		if (button === 1)
+			Engine.ConnectXmppClient();
 	}
 }
Index: binaries/data/mods/public/gui/lobby/LobbyPage/LobbyPage.js
===================================================================
--- binaries/data/mods/public/gui/lobby/LobbyPage/LobbyPage.js
+++ binaries/data/mods/public/gui/lobby/LobbyPage/LobbyPage.js
@@ -4,7 +4,7 @@
  */
 class LobbyPage
 {
-	constructor(dialog, xmppMessages, leaderboardPage, profilePage)
+	constructor(dialog, xmppMessages, leaderboardPage, profilePage, resolve)
 	{
 		Engine.ProfileStart("Create LobbyPage");
 		let mapCache = new MapCache();
@@ -19,7 +19,7 @@
 				"joinButton": new JoinButton(dialog, gameList),
 				"leaderboardButton": new LeaderboardButton(xmppMessages, leaderboardPage),
 				"profileButton": new ProfileButton(xmppMessages, profilePage),
-				"quitButton": new QuitButton(dialog, leaderboardPage, profilePage)
+				"quitButton": new QuitButton(dialog, leaderboardPage, profilePage, resolve)
 			},
 			"panels": {
 				"chatPanel": new ChatPanel(xmppMessages),
Index: binaries/data/mods/public/gui/lobby/lobby.js
===================================================================
--- binaries/data/mods/public/gui/lobby/lobby.js
+++ binaries/data/mods/public/gui/lobby/lobby.js
@@ -33,8 +33,13 @@
  */
 function init(attribs)
 {
-	if (g_Settings)
-		g_LobbyHandler = new LobbyHandler(attribs && attribs.dialog);
-	else
-		error("Could not load settings");
+	return new Promise(resolve => {
+		if (g_Settings)
+			g_LobbyHandler = new LobbyHandler(attribs && attribs.dialog, resolve);
+		else
+		{
+			error("Could not load settings");
+			resolve();
+		}
+	});
 }
Index: binaries/data/mods/public/gui/locale/locale.js
===================================================================
--- binaries/data/mods/public/gui/locale/locale.js
+++ binaries/data/mods/public/gui/locale/locale.js
@@ -21,11 +21,8 @@
 		localeText.caption = "long";
 	else
 		localeText.caption = currentLocale;
-}
 
-function cancelSetup()
-{
-	Engine.PopGuiPage();
+	return new Promise(resolve => Engine.GetGUIObjectByName("cancelButton").onPress = resolve);
 }
 
 function applySelectedLocale()
Index: binaries/data/mods/public/gui/locale/locale.xml
===================================================================
--- binaries/data/mods/public/gui/locale/locale.xml
+++ binaries/data/mods/public/gui/locale/locale.xml
@@ -32,9 +32,8 @@
 			</object>
 			<object name="localeText" type="text" size="40%+10 80 100% 105" textcolor="white" />
 
-			<object type="button" size="0 100%-60 33% 100%-32" style="ModernButtonRed" hotkey="cancel">
+			<object name="cancelButton" type="button" size="0 100%-60 33% 100%-32" style="ModernButtonRed" hotkey="cancel">
 				<translatableAttribute id="caption">Cancel</translatableAttribute>
-				<action on="Press">cancelSetup();</action>
 			</object>
 
 			<object type="button" size="33%+5 100%-60 66% 100%-32" style="ModernButtonRed">
Index: binaries/data/mods/public/gui/locale_advanced/locale_advanced.js
===================================================================
--- binaries/data/mods/public/gui/locale_advanced/locale_advanced.js
+++ binaries/data/mods/public/gui/locale_advanced/locale_advanced.js
@@ -46,6 +46,12 @@
 
 	// fill the script
 	scriptInput.caption = Engine.GetLocaleScript(initData.locale);
+
+	return new Promise(resolve => {
+		Engine.GetGUIObjectByName("cancelButton").onPress = resolve);
+		Engine.GetGUIObjectByName("acceptButton").onPress = () =>
+			resolve(Engine.GetGUIObjectByName("resultingLocale").caption);
+	});
 }
 
 // TODO: an onChanged event for input boxes would be useful and would allow us to avoid a tick event here.
@@ -54,11 +60,6 @@
 	updateResultingLocale();
 }
 
-function cancelSetup()
-{
-	Engine.PopGuiPage();
-}
-
 function updateResultingLocale()
 {
 	var languageList = Engine.GetGUIObjectByName("languageList");
@@ -110,9 +111,3 @@
 	countryList.selected = countryList.list_data.indexOf(Engine.GetLocaleCountry(locale));
 	scriptInput.caption = Engine.GetLocaleScript(locale);
 }
-
-function applySelectedLocale()
-{
-	var resultingLocaleText = Engine.GetGUIObjectByName("resultingLocale");
-	Engine.PopGuiPage(resultingLocaleText.caption);
-}
Index: binaries/data/mods/public/gui/locale_advanced/locale_advanced.xml
===================================================================
--- binaries/data/mods/public/gui/locale_advanced/locale_advanced.xml
+++ binaries/data/mods/public/gui/locale_advanced/locale_advanced.xml
@@ -61,9 +61,8 @@
 			</object>
 			<object name="dictionaryFile" type="text" size="50%+10 260 100% 345" style="ModernText" />
 
-			<object type="button" size="0 100%-60 33% 100%-25" style="ModernButtonRed" hotkey="cancel">
+			<object name="cancelButton" type="button" size="0 100%-60 33% 100%-25" style="ModernButtonRed" hotkey="cancel">
 				<translatableAttribute id="caption">Cancel</translatableAttribute>
-				<action on="Press">cancelSetup();</action>
 			</object>
 
 			<object type="button" size="33%+5 100%-60 66% 100%-25" style="ModernButtonRed">
Index: binaries/data/mods/public/gui/manual/manual.js
===================================================================
--- binaries/data/mods/public/gui/manual/manual.js
+++ binaries/data/mods/public/gui/manual/manual.js
@@ -7,4 +7,6 @@
 
 	// Replace anything starting with 'hotkey.' with its hotkey.
 	mainText.caption = text.replace(/hotkey\.([a-z0-9_\.]+)/g, (_, k) => formatHotkeyCombinations(hotkeys[k]));
+
+	return new Promise(resolve => Engine.GetGUIObjectByName("cancelButton").onPress = resolve);
 }
Index: binaries/data/mods/public/gui/manual/manual.xml
===================================================================
--- binaries/data/mods/public/gui/manual/manual.xml
+++ binaries/data/mods/public/gui/manual/manual.xml
@@ -17,9 +17,8 @@
 			<object name="mainText" type="text" style="ModernTextPanel" />
 		</object>
 
-		<object type="button" style="ModernButtonRed" tooltip_style="snToolTip" size="100%-408 100%-52 100%-218 100%-24" hotkey="cancel">
+		<object name="cancelButton" type="button" style="ModernButtonRed" tooltip_style="snToolTip" size="100%-408 100%-52 100%-218 100%-24" hotkey="cancel">
 			<translatableAttribute id="caption">Close</translatableAttribute>
-			<action on="Press">Engine.PopGuiPage();</action>
 		</object>
 
 		<object name="url" type="button" style="ModernButtonRed" size="100%-214 100%-52 100%-24 100%-24">
Index: binaries/data/mods/public/gui/maps/mapbrowser/MapBrowserPage.js
===================================================================
--- binaries/data/mods/public/gui/maps/mapbrowser/MapBrowserPage.js
+++ binaries/data/mods/public/gui/maps/mapbrowser/MapBrowserPage.js
@@ -8,7 +8,7 @@
 	let cache = new MapCache();
 	let filters = new MapFilters(cache);
 	let browser = new MapBrowser(cache, filters);
-	browser.registerClosePageHandler(() => Engine.PopGuiPage());
 	browser.openPage(false);
 	browser.controls.MapFiltering.select("default", "skirmish");
+	return new Promise(browser.registerClosePageHandler.bind(browser));
 }
Index: binaries/data/mods/public/gui/options/options.js
===================================================================
--- binaries/data/mods/public/gui/options/options.js
+++ binaries/data/mods/public/gui/options/options.js
@@ -173,18 +173,19 @@
 				control.tooltip = item && item.tooltip || option.tooltip;
 			};
 		},
-		"timeout": (option, oldValue, hasChanges, newValue) => {
+		"timeout": async (option, oldValue, hasChanges, newValue) => {
 			if (!option.timeout)
 				return;
-			timedConfirmation(
+			const button = await timedConfirmation(
 				500, 200,
 				translate("Changes will be reverted in %(time)s seconds. Do you want to keep changes?"),
 				"time",
 				option.timeout,
 				translate("Warning"),
-				[translate("No"), translate("Yes")],
-				[() => {this.revertChange(option, +oldValue, hasChanges);}, null]
-			);
+				[translate("No"), translate("Yes")]);
+
+			if (button === 0)
+				this.revertChange(option, +oldValue, hasChanges);
 		}
 	},
 	"slider":
@@ -224,6 +225,11 @@
 		g_TabButtonDist,
 		selectPanel,
 		displayOptions);
+
+	return new Promise(resolve => {
+		Engine.GetGUIObjectByName("closeButton").onPress = async() =>
+			await shouldClosePage() && resolve();
+	});
 }
 
 function getHotloadData()
@@ -354,19 +360,17 @@
 	Engine.GetGUIObjectByName("saveChanges").enabled = hasChanges;
 }
 
-function setDefaults()
+async function setDefaults()
 {
-	messageBox(
+	const button = await messageBox(
 		500, 200,
 		translate("Resetting the options will erase your saved settings. Do you want to continue?"),
 		translate("Warning"),
-		[translate("No"), translate("Yes")],
-		[null, reallySetDefaults]
-	);
-}
+		[translate("No"), translate("Yes")])
+
+	if (button === 0)
+		return;
 
-function reallySetDefaults()
-{
 	for (let category in g_Options)
 		for (let option of g_Options[category].options)
 		{
@@ -405,7 +409,7 @@
 	displayOptions();
 }
 
-function saveChanges()
+async function saveChanges()
 {
 	for (let category in g_Options)
 		for (let i = 0; i < g_Options[category].options.length; ++i)
@@ -421,13 +425,14 @@
 
 			selectPanel(category);
 
-			messageBox(
+			const button = await messageBox(
 				500, 200,
 				translate("Some setting values are invalid! Are you sure you want to save them?"),
 				translate("Warning"),
-				[translate("No"), translate("Yes")],
-				[null, reallySaveChanges]
-			);
+				[translate("No"), translate("Yes")]);
+
+			if (button === 1)
+				reallySaveChanges();
 			return;
 		}
 
@@ -440,23 +445,15 @@
 	enableButtons();
 }
 
-/**
- * Close GUI page and inform the parent GUI page which options changed.
- **/
-function closePage()
+async function shouldClosePage()
 {
-	if (Engine.ConfigDB_HasChanges("user"))
-		messageBox(
-			500, 200,
-			translate("You have unsaved changes, do you want to close this window?"),
-			translate("Warning"),
-			[translate("No"), translate("Yes")],
-			[null, closePageWithoutConfirmation]);
-	else
-		closePageWithoutConfirmation();
-}
+	if (!Engine.ConfigDB_HasChanges("user"))
+		return true;
 
-function closePageWithoutConfirmation()
-{
-	Engine.PopGuiPage(g_ChangedKeys);
+	const button = await messageBox(
+		500, 200,
+		translate("You have unsaved changes, do you want to close this window?"),
+		translate("Warning"),
+		[translate("No"), translate("Yes")]);
+	return button === 1;
 }
Index: binaries/data/mods/public/gui/options/options.xml
===================================================================
--- binaries/data/mods/public/gui/options/options.xml
+++ binaries/data/mods/public/gui/options/options.xml
@@ -58,10 +58,9 @@
 			<action on="Press">saveChanges();</action>
 		</object>
 
-		<object type="button" style="ModernButtonRed" size="50%+186 100%-44 50%+336 100%-16" hotkey="cancel">
+		<object name="closeButton" type="button" style="ModernButtonRed" size="50%+186 100%-44 50%+336 100%-16" hotkey="cancel">
 			<translatableAttribute id="caption">Close</translatableAttribute>
 			<translatableAttribute id="tooltip">Unsaved changes affect this session only</translatableAttribute>
-			<action on="Press">closePage();</action>
 		</object>
 
 	</object>
Index: binaries/data/mods/public/gui/pregame/MainMenuItems.js
===================================================================
--- binaries/data/mods/public/gui/pregame/MainMenuItems.js
+++ binaries/data/mods/public/gui/pregame/MainMenuItems.js
@@ -259,14 +259,18 @@
 	{
 		"caption": translate("Scenario Editor"),
 		"tooltip": translate('Open the Atlas Scenario Editor in a new window. You can run this more reliably by starting the game with the command-line argument "-editor".'),
-		"onPress": () => {
+		"onPress": async () => {
 			if (Engine.AtlasIsAvailable())
-				messageBox(
+			{
+				const button = messageBox(
 					400, 200,
 					translate("Are you sure you want to quit 0 A.D. and open the Scenario Editor?"),
 					translate("Confirmation"),
-					[translate("No"), translate("Yes")],
-					[null, Engine.RestartInAtlas]);
+					[translate("No"), translate("Yes")]);
+
+				if (button === 1)
+					Engine.RestartInAtlas();
+			}
 			else
 				messageBox(
 					400, 200,
@@ -284,13 +288,15 @@
 	{
 		"caption": translate("Exit"),
 		"tooltip": translate("Exit the game."),
-		"onPress": () => {
-			messageBox(
+		"onPress": async () => {
+			const button = await messageBox(
 				400, 200,
 				translate("Are you sure you want to quit 0 A.D.?"),
 				translate("Confirmation"),
-				[translate("No"), translate("Yes")],
-				[null, Engine.Exit]);
+				[translate("No"), translate("Yes")]);
+
+			if (button === 1)
+				Engine.Exit();
 		}
 	}
 ];
Index: binaries/data/mods/public/gui/pregame/mainmenu.js
===================================================================
--- binaries/data/mods/public/gui/pregame/mainmenu.js
+++ binaries/data/mods/public/gui/pregame/mainmenu.js
@@ -18,6 +18,8 @@
 			g_BackgroundLayerData,
 			g_ProjectInformation,
 			g_CommunityButtons);
+
+	return new Promise(() => {});
 }
 
 function getHotloadData()
Index: binaries/data/mods/public/gui/prelobby/common/credentials/credentials.js
===================================================================
--- binaries/data/mods/public/gui/prelobby/common/credentials/credentials.js
+++ binaries/data/mods/public/gui/prelobby/common/credentials/credentials.js
@@ -44,22 +44,25 @@
 		Engine.ConfigDB_GetValue("user", "lobby.rememberpassword") == "true";
 }
 
-function toggleRememberPassword()
+async function toggleRememberPassword()
 {
 	let checkbox = Engine.GetGUIObjectByName("rememberPassword");
 	let enabled = Engine.ConfigDB_GetValue("user", "lobby.rememberpassword") == "true";
 	if (!checkbox.checked && enabled && Engine.ConfigDB_GetValue("user", "lobby.password"))
-		messageBox(
+	{
+		const button = messageBox(
 			360, 160,
 			translate("Are you sure you want to delete the password after connecting?"),
 			translate("Confirmation"),
-			[translate("No"), translate("Yes")],
-			[
-				() => { checkbox.checked = true; },
-				() => { Engine.ConfigDB_CreateAndSaveValue("user", "lobby.rememberpassword", String(!enabled)); }
-			]);
-	else
-		Engine.ConfigDB_CreateAndSaveValue("user", "lobby.rememberpassword", String(!enabled));
+			[translate("No"), translate("Yes")]);
+
+		if (button === 0)
+		{
+			checkbox.checked = true;
+			return
+		}
+	}
+	Engine.ConfigDB_CreateAndSaveValue("user", "lobby.rememberpassword", String(!enabled));
 }
 
 function getEncryptedPassword()
Index: binaries/data/mods/public/gui/prelobby/common/feedback/feedback.js
===================================================================
--- binaries/data/mods/public/gui/prelobby/common/feedback/feedback.js
+++ binaries/data/mods/public/gui/prelobby/common/feedback/feedback.js
@@ -37,9 +37,8 @@
 	Engine.GetGUIObjectByName("continue").enabled = !feedbackText;
 }
 
-function cancelButton()
+function cancelButton(closePage)
 {
 	if (Engine.HasXmppClient())
 		Engine.StopXmppClient();
-	Engine.PopGuiPage();
 }
Index: binaries/data/mods/public/gui/prelobby/entrance/entrance.js
===================================================================
--- binaries/data/mods/public/gui/prelobby/entrance/entrance.js
+++ binaries/data/mods/public/gui/prelobby/entrance/entrance.js
@@ -2,6 +2,8 @@
 {
 	if (Engine.ConfigDB_GetValue("user", "lobby.login"))
 		loginButton();
+
+	return new Promise(resolve => Engine.GetGUIObjectByName("cancel").onPress = resolve);
 }
 
 function loginButton()
@@ -13,8 +15,3 @@
 {
 	Engine.PushGuiPage("page_prelobby_register.xml");
 }
-
-function cancelButton()
-{
-	Engine.PopGuiPage();
-}
Index: binaries/data/mods/public/gui/prelobby/entrance/entrance.xml
===================================================================
--- binaries/data/mods/public/gui/prelobby/entrance/entrance.xml
+++ binaries/data/mods/public/gui/prelobby/entrance/entrance.xml
@@ -28,7 +28,6 @@
 
 			<object name="cancel" type="button" size="18 100%-45 50%-5 100%-17" style="ModernButtonRed" hotkey="cancel">
 				<translatableAttribute id="caption">Cancel</translatableAttribute>
-				<action on="Press">cancelButton();</action>
 			</object>
 
 		</object>
Index: binaries/data/mods/public/gui/prelobby/login/login.js
===================================================================
--- binaries/data/mods/public/gui/prelobby/login/login.js
+++ binaries/data/mods/public/gui/prelobby/login/login.js
@@ -13,6 +13,13 @@
 	initRememberPassword();
 
 	updateFeedback();
+
+	return new Promise(resolve => {
+		Engine.GetGUIObjectByName("cancel").onPress = () => {
+			cancelButton();
+			resolve();
+		};
+	});
 }
 
 function updateFeedback()
Index: binaries/data/mods/public/gui/prelobby/register/register.js
===================================================================
--- binaries/data/mods/public/gui/prelobby/register/register.js
+++ binaries/data/mods/public/gui/prelobby/register/register.js
@@ -1,6 +1,11 @@
 function init()
 {
-	g_LobbyMessages.registered = onRegistered;
+	const continued = newPromise(resolve =>
+		g_LobbyMessages.registered = () => {
+			onRegistered();
+			resolve();
+		};
+	);
 
 	Engine.GetGUIObjectByName("continue").caption = translate("Register");
 
@@ -9,6 +14,14 @@
 	initRememberPassword();
 
 	updateFeedback();
+
+	const canceled = new Promise(resolve =>
+		Engine.GetGUIObjectByName("cancel").onPress = () => {
+			cancelButton();
+			resolve();
+		};
+	);
+	return Promise.race([continued, canceled]);
 }
 
 function updateFeedback()
@@ -40,6 +53,5 @@
 
 	Engine.StopXmppClient();
 
-	Engine.PopGuiPage();
 	Engine.PushGuiPage("page_prelobby_login.xml");
 }
Index: binaries/data/mods/public/gui/reference/catafalque/CatafalquePage.js
===================================================================
--- binaries/data/mods/public/gui/reference/catafalque/CatafalquePage.js
+++ binaries/data/mods/public/gui/reference/catafalque/CatafalquePage.js
@@ -1,6 +1,6 @@
 class CatafalquePage extends ReferencePage
 {
-	constructor(data)
+	constructor(closePage)
 	{
 		super();
 
@@ -26,14 +26,8 @@
 				canvasCenterY + radius * -Math.cos(angle * i)
 			);
 
-		let closeButton = new CloseButton(this);
+		closePage(closeButton(this.CloseButtonTooltip));
 	}
-
-	closePage()
-	{
-		Engine.PopGuiPage({ "page": "page_catafalque.xml" });
-	}
-
 }
 
 
Index: binaries/data/mods/public/gui/reference/catafalque/catafalque.js
===================================================================
--- binaries/data/mods/public/gui/reference/catafalque/catafalque.js
+++ binaries/data/mods/public/gui/reference/catafalque/catafalque.js
@@ -1,4 +1,4 @@
-function init(data = {})
+function init()
 {
-	g_Page = new CatafalquePage(data);
+	return new Promise(resolve => g_Page = new CatafalquePage(resolve));
 }
Index: binaries/data/mods/public/gui/reference/civinfo/CivInfoPage.js
===================================================================
--- binaries/data/mods/public/gui/reference/civinfo/CivInfoPage.js
+++ binaries/data/mods/public/gui/reference/civinfo/CivInfoPage.js
@@ -1,6 +1,6 @@
 class CivInfoPage extends ReferencePage
 {
-	constructor(data)
+	constructor(closePage)
 	{
 		super();
 
@@ -10,29 +10,22 @@
 		this.gameplaySection = new GameplaySection(this);
 		this.historySection = new HistorySection(this);
 
-		let structreeButton = new StructreeButton(this);
-		let closeButton = new CloseButton(this);
-		Engine.SetGlobalHotkey("civinfo", "Press", this.closePage.bind(this));
-	}
-
-	switchToStructreePage()
-	{
-		Engine.PopGuiPage({
+		structreeButton().then(closePage.bind(null, {
 			"nextPage": "page_structree.xml",
 			"args": {
 				"civ": this.activeCiv
 			}
-		});
-	}
+		}));
 
-	closePage()
-	{
-		Engine.PopGuiPage({
+		Promise.race([
+			closeButton(this.CloseButtonTooltip),
+			new Promise(resolve => Engine.SetGlobalHotkey("civinfo", "Press", resolve))
+		]).then(closePage.bind(null, {
 			"page": "page_civinfo.xml",
 			"args": {
 				"civ": this.activeCiv
 			}
-		});
+		}));
 	}
 
 	/**
Index: binaries/data/mods/public/gui/reference/civinfo/civinfo.js
===================================================================
--- binaries/data/mods/public/gui/reference/civinfo/civinfo.js
+++ binaries/data/mods/public/gui/reference/civinfo/civinfo.js
@@ -3,10 +3,12 @@
  */
 function init(data = {})
 {
-	g_Page = new CivInfoPage(data);
+	return new Promise(resolve => {
+		g_Page = new CivInfoPage(resolve);
 
-	if (data.civ)
-		g_Page.civSelection.selectCiv(data.civ);
-	else
-		g_Page.civSelection.selectFirstCiv();
+		if (data.civ)
+			g_Page.civSelection.selectCiv(data.civ);
+		else
+			g_Page.civSelection.selectFirstCiv();
+	});
 }
Index: binaries/data/mods/public/gui/reference/common/Buttons/CivInfoButton.js
===================================================================
--- binaries/data/mods/public/gui/reference/common/Buttons/CivInfoButton.js
+++ binaries/data/mods/public/gui/reference/common/Buttons/CivInfoButton.js
@@ -1,32 +1,9 @@
-class CivInfoButton
+function civInfoButton()
 {
-	constructor(parentPage)
-	{
-		this.parentPage = parentPage;
-
-		this.civInfoButton = Engine.GetGUIObjectByName("civInfoButton");
-		this.civInfoButton.onPress = this.onPress.bind(this);
-		this.civInfoButton.caption = this.Caption;
-		this.civInfoButton.tooltip = colorizeHotkey(this.Tooltip, this.Hotkey);
-	}
-
-	onPress()
-	{
-		Engine.PopGuiPage({
-			"nextPage": "page_civinfo.xml",
-			"args": {
-				"civ": this.parentPage.activeCiv
-			}
-		});
-	}
+	const button = Engine.GetGUIObjectByName("civInfoButton");
+	button.caption = translate("Civilization Overview");;
+	button.tooltip =
+		colorizeHotkey(translate("%(hotkey)s: Switch to Civilization Overview."), "civinfo");
 
+	return new Promise(resolve => button.onPress = resolve);
 }
-
-CivInfoButton.prototype.Caption =
-	translate("Civilization Overview");
-
-CivInfoButton.prototype.Hotkey =
-	"civinfo";
-
-CivInfoButton.prototype.Tooltip =
-	translate("%(hotkey)s: Switch to Civilization Overview.");
Index: binaries/data/mods/public/gui/reference/common/Buttons/CloseButton.js
===================================================================
--- binaries/data/mods/public/gui/reference/common/Buttons/CloseButton.js
+++ binaries/data/mods/public/gui/reference/common/Buttons/CloseButton.js
@@ -1,16 +1,7 @@
-class CloseButton
+function closeButton(tooltip)
 {
-	constructor(parentPage)
-	{
-		this.closeButton = Engine.GetGUIObjectByName("closeButton");
-		this.closeButton.onPress = parentPage.closePage.bind(parentPage);
-		this.closeButton.caption = this.Caption;
-		this.closeButton.tooltip = colorizeHotkey(parentPage.CloseButtonTooltip, this.Hotkey);
-	}
+	const button = Engine.GetGUIObjectByName("closeButton");
+	button.caption = translate("Close");
+	button.tooltip = colorizeHotkey(tooltip, "cancel");
+	return new Promise(resolve => button.onPress = resolve);
 }
-
-CloseButton.prototype.Caption =
-	translate("Close");
-
-CloseButton.prototype.Hotkey =
-	"cancel";
Index: binaries/data/mods/public/gui/reference/common/Buttons/StructreeButton.js
===================================================================
--- binaries/data/mods/public/gui/reference/common/Buttons/StructreeButton.js
+++ binaries/data/mods/public/gui/reference/common/Buttons/StructreeButton.js
@@ -1,32 +1,9 @@
-class StructreeButton
+function structreeButton()
 {
-	constructor(parentPage)
-	{
-		this.parentPage = parentPage;
-
-		this.civInfoButton = Engine.GetGUIObjectByName("structreeButton");
-		this.civInfoButton.onPress = this.onPress.bind(this);
-		this.civInfoButton.caption = this.Caption;
-		this.civInfoButton.tooltip = colorizeHotkey(this.Tooltip, this.Hotkey);
-	}
-
-	onPress()
-	{
-		Engine.PopGuiPage({
-			"nextPage": "page_structree.xml",
-			"args": {
-				"civ": this.parentPage.activeCiv
-			}
-		});
-	}
+	const civInfoButton = Engine.GetGUIObjectByName("structreeButton");
+	civInfoButton.caption = translate("Structure Tree");
+	civInfoButton.tooltip =
+		colorizeHotkey(translate("%(hotkey)s: Switch to Structure Tree."), "structree");
 
+	return new Promise(resolve => civInfoButton.onPress = resolve);
 }
-
-StructreeButton.prototype.Caption =
-	translate("Structure Tree");
-
-StructreeButton.prototype.Hotkey =
-	"structree";
-
-StructreeButton.prototype.Tooltip =
-	translate("%(hotkey)s: Switch to Structure Tree.");
Index: binaries/data/mods/public/gui/reference/structree/StructreePage.js
===================================================================
--- binaries/data/mods/public/gui/reference/structree/StructreePage.js
+++ binaries/data/mods/public/gui/reference/structree/StructreePage.js
@@ -5,7 +5,7 @@
  */
 class StructreePage extends ReferencePage
 {
-	constructor(data)
+	constructor(data, closePage)
 	{
 		super();
 
@@ -21,30 +21,34 @@
 		this.TrainerSection = new TrainerSection(this);
 		this.TreeSection = new TreeSection(this);
 
+		const boundClosePage = () => closePage({
+			"page": "page_structree.xml",
+			"args": {
+				"civ": this.activeCiv
+			}
+		});
+
 		this.civSelection = new CivSelectDropdown(this.civData);
 		if (!this.civSelection.hasCivs())
 		{
-			this.closePage();
+			boundClosePage();
 			return;
 		}
 		this.civSelection.registerHandler(this.selectCiv.bind(this));
 
-		let civInfoButton = new CivInfoButton(this);
-		let closeButton = new CloseButton(this);
-		Engine.SetGlobalHotkey("structree", "Press", this.closePage.bind(this));
+		civInfoButton().then(closePage.bind(null, {
+			"nextPage": "page_civinfo.xml",
+			"args": {
+				"civ": this.activeCiv
+			}
+		}));
 
 		this.StructreePage.onWindowResized = this.updatePageWidth.bind(this);
 		this.width = 0;
-	}
 
-	closePage()
-	{
-		Engine.PopGuiPage({
-			"page": "page_structree.xml",
-			"args": {
-				"civ": this.activeCiv
-			}
-		});
+		Promise.race([closeButton(this.CloseButtonTooltip),
+			new Promise(resolve => Engine.SetGlobalHotkey("structree", "Press", resolve))
+		]).then(boundClosePage);
 	}
 
 	selectCiv(civCode)
Index: binaries/data/mods/public/gui/reference/structree/structree.js
===================================================================
--- binaries/data/mods/public/gui/reference/structree/structree.js
+++ binaries/data/mods/public/gui/reference/structree/structree.js
@@ -5,10 +5,12 @@
  */
 function init(data = {})
 {
-	g_Page = new StructreePage(data);
+	return new Promise(resolve => {
+		g_Page = new StructreePage(data, resolve);
 
-	if (data.civ)
-		g_Page.civSelection.selectCiv(data.civ);
-	else
-		g_Page.civSelection.selectFirstCiv();
+		if (data.civ)
+			g_Page.civSelection.selectCiv(data.civ);
+		else
+			g_Page.civSelection.selectFirstCiv();
+	});
 }
Index: binaries/data/mods/public/gui/reference/viewer/ViewerPage.js
===================================================================
--- binaries/data/mods/public/gui/reference/viewer/ViewerPage.js
+++ binaries/data/mods/public/gui/reference/viewer/ViewerPage.js
@@ -3,7 +3,7 @@
  */
 class ViewerPage extends ReferencePage
 {
-	constructor(data)
+	constructor(closePage)
 	{
 		super();
 
@@ -17,7 +17,9 @@
 			"entityRankGlyph": Engine.GetGUIObjectByName("entityRankGlyph"),
 		};
 
-		let closeButton = new CloseButton(this);
+		this.closePage = closePage;
+
+		closeButton(this.CloseButtonTooltip).then(closePage);
 	}
 
 	selectTemplate(data)
@@ -137,11 +139,6 @@
 			this.guiElements.entityRankGlyph.sprite = "stretched:" + this.RankIconPath + this.currentTemplate.promotion.current_rank + ".png";
 		this.guiElements.entityRankGlyph.hidden = !this.currentTemplate.promotion;
 	}
-
-	closePage()
-	{
-		Engine.PopGuiPage({ "civ": this.activeCiv, "page": "page_viewer.xml" });
-	}
 }
 
 /**
Index: binaries/data/mods/public/gui/reference/viewer/viewer.js
===================================================================
--- binaries/data/mods/public/gui/reference/viewer/viewer.js
+++ binaries/data/mods/public/gui/reference/viewer/viewer.js
@@ -14,6 +14,7 @@
  */
 function init(data)
 {
-	g_Page = new ViewerPage();
+	const promise = new Promise(resolve => g_Page = new ViewerPage(resolve));
 	g_Page.selectTemplate(data);
+	return promise;
 }
Index: binaries/data/mods/public/gui/replaymenu/replay_actions.js
===================================================================
--- binaries/data/mods/public/gui/replaymenu/replay_actions.js
+++ binaries/data/mods/public/gui/replaymenu/replay_actions.js
@@ -161,7 +161,7 @@
 /**
  * Shows a confirmation dialog and deletes the selected replay from the disk in case.
  */
-function deleteReplay()
+async function deleteReplay()
 {
 	// Get selected replay
 	var selected = Engine.GetGUIObjectByName("replaySelection").selected;
@@ -170,14 +170,15 @@
 
 	var replay = g_ReplaysFiltered[selected];
 
-	messageBox(
+	const button = await messageBox(
 		500, 200,
 		translate("Are you sure you want to delete this replay permanently?") + "\n" +
 			escapeText(Engine.GetReplayDirectoryName(replay.directory)),
 		translate("Delete replay"),
-		[translate("No"), translate("Yes")],
-		[null, function() { reallyDeleteReplay(replay.directory); }]
-	);
+		[translate("No"), translate("Yes")]);
+
+	if (button === 1)
+		reallyDeleteReplay(replay.directory);
 }
 
 /**
Index: binaries/data/mods/public/gui/replaymenu/replay_menu.js
===================================================================
--- binaries/data/mods/public/gui/replaymenu/replay_menu.js
+++ binaries/data/mods/public/gui/replaymenu/replay_menu.js
@@ -78,6 +78,8 @@
 
 	initHotkeyTooltips();
 	displayReplayList();
+
+	return new Promise(() => {});
 }
 
 /**
Index: binaries/data/mods/public/gui/session/campaigns/CampaignSession.js
===================================================================
--- binaries/data/mods/public/gui/session/campaigns/CampaignSession.js
+++ binaries/data/mods/public/gui/session/campaigns/CampaignSession.js
@@ -1,9 +1,9 @@
 class CampaignSession
 {
-	constructor(data)
+	constructor(data, closePage)
 	{
 		this.run = new CampaignRun(data.run).load();
-		registerPlayersFinishedHandler(this.onFinish.bind(this));
+		registerPlayersFinishedHandler(this.onFinish.bind(this, closePage));
 		this.endGameData = {
 			"won": false,
 			"initData": data,
@@ -11,7 +11,7 @@
 		};
 	}
 
-	onFinish(players, won)
+	onFinish(closePage, players, won)
 	{
 		let playerID = Engine.GetPlayerID();
 		if (players.indexOf(playerID) === -1)
@@ -24,7 +24,7 @@
 
 		// Run the endgame script.
 		Engine.PushGuiPage(this.getEndGame(), this.endGameData);
-		Engine.PopGuiPage();
+		closePage();
 	}
 
 	getMenu()
Index: binaries/data/mods/public/gui/session/session.js
===================================================================
--- binaries/data/mods/public/gui/session/session.js
+++ binaries/data/mods/public/gui/session/session.js
@@ -270,8 +270,10 @@
 			restoreSavedGameData(initData.savedGUIData);
 	}
 
-	if (g_InitAttributes.campaignData)
-		g_CampaignSession = new CampaignSession(g_InitAttributes.campaignData);
+	const promise = new Promise(resolve => {
+		if (g_InitAttributes.campaignData)
+			g_CampaignSession = new CampaignSession(g_InitAttributes.campaignData, resolve);
+	});
 
 	let mapCache = new MapCache();
 	g_Cheats = new Cheats();
@@ -332,6 +334,7 @@
 	onSimulationUpdate();
 
 	setTimeout(displayGamestateNotifications, 1000);
+	return promise;
 }
 
 function registerPlayersInitHandler(handler)
Index: binaries/data/mods/public/gui/session/top_panel/CivIcon.js
===================================================================
--- binaries/data/mods/public/gui/session/top_panel/CivIcon.js
+++ binaries/data/mods/public/gui/session/top_panel/CivIcon.js
@@ -29,7 +29,7 @@
 		this.openPage(this.dialogSelection.page);
 	}
 
-	openPage(page)
+	async openPage(page)
 	{
 		closeOpenDialogs();
 		g_PauseControl.implicitPause();
Index: binaries/data/mods/public/gui/splashscreen/splashscreen.js
===================================================================
--- binaries/data/mods/public/gui/splashscreen/splashscreen.js
+++ binaries/data/mods/public/gui/splashscreen/splashscreen.js
@@ -1,15 +1,19 @@
 var g_SplashScreenFile = "gui/splashscreen/splashscreen.txt";
 
-function init(data)
+async function init(data)
 {
 	Engine.GetGUIObjectByName("mainText").caption = Engine.TranslateLines(Engine.ReadFile(g_SplashScreenFile));
 	Engine.GetGUIObjectByName("displaySplashScreen").checked = Engine.ConfigDB_GetValue("user", "gui.splashscreen.enable") === "true";
-}
 
-function closePage()
-{
-	Engine.ConfigDB_CreateValue("user", "gui.splashscreen.enable", String(Engine.GetGUIObjectByName("displaySplashScreen").checked));
-	Engine.ConfigDB_CreateValue("user", "gui.splashscreen.version", Engine.GetFileMTime(g_SplashScreenFile));
+	await new Promise(resolve => Engine.GetGUIObjectByName("btnOK").onPress = resolve);
+
+	Engine.ConfigDB_CreateValue(
+		"user",
+		"gui.splashscreen.enable",
+		String(Engine.GetGUIObjectByName("displaySplashScreen").checked));
+	Engine.ConfigDB_CreateValue(
+		"user",
+		"gui.splashscreen.version",
+		Engine.GetFileMTime(g_SplashScreenFile));
 	Engine.ConfigDB_SaveChanges("user");
-	Engine.PopGuiPage();
 }
Index: binaries/data/mods/public/gui/splashscreen/splashscreen.xml
===================================================================
--- binaries/data/mods/public/gui/splashscreen/splashscreen.xml
+++ binaries/data/mods/public/gui/splashscreen/splashscreen.xml
@@ -23,7 +23,6 @@
 
 		<object name="btnOK" type="button" style="ModernButtonRed" size="18 100%-45 50%-5 100%-17" hotkey="cancel">
 			<translatableAttribute id="caption">OK</translatableAttribute>
-			<action on="Press">closePage();</action>
 		</object>
 
 		<object type="button" style="ModernButtonRed" size="50%+5 100%-45 100%-18 100%-17">
Index: binaries/data/mods/public/gui/summary/summary.js
===================================================================
--- binaries/data/mods/public/gui/summary/summary.js
+++ binaries/data/mods/public/gui/summary/summary.js
@@ -139,6 +139,10 @@
 {
 	initSummaryData(data);
 	initGUISummary();
+
+	return new Promise(resolve => {
+		Engine.GetGUIObjectByName("continueButton").onPress = continueButton(resolve);
+	});
 }
 
 function initSummaryData(data)
@@ -453,7 +457,7 @@
 		updateCountersTeam(teamCounterFn, panelInfo.counters, panelInfo.headings, index);
 }
 
-function continueButton()
+function continueButton(resolve)
 {
 	let summarySelection = {
 		"panel": g_TabCategorySelected,
@@ -461,11 +465,11 @@
 		"teamCharts": Engine.GetGUIObjectByName("toggleTeamBox").checked
 	};
 	if (g_GameData.gui.isInGame)
-		Engine.PopGuiPage({
+		resolve({
 			"summarySelection": summarySelection
 		});
 	else if (g_GameData.gui.dialog)
-		Engine.PopGuiPage();
+		resolve();
 	else if (Engine.HasXmppClient())
 		Engine.SwitchGuiPage("page_lobby.xml", { "dialog": false });
 	else if (g_GameData.gui.isReplay)
Index: binaries/data/mods/public/gui/summary/summary.xml
===================================================================
--- binaries/data/mods/public/gui/summary/summary.xml
+++ binaries/data/mods/public/gui/summary/summary.xml
@@ -5,17 +5,6 @@
 	<script directory="gui/common/"/>
 	<script directory="gui/summary/"/>
 
-	<object hotkey="summary">
-		<action on="Press">continueButton();</action>
-	</object>
-
-	<object hotkey="cancel">
-		<action on="Press">
-		if (g_GameData.gui.isInGame)
-			continueButton();
-		</action>
-	</object>
-
 	<object type="image" sprite="ModernFade" name="fadeImage"/>
 
 	<object name="summaryWindow"
@@ -112,7 +101,7 @@
 				</repeat>
 			</object>
 		</object>
-		
+
 		<object name="chartsPanel" type="image" sprite="ModernTabHorizontalFrame" size="20 120 100%-20 100%-54">
 			<repeat count="2" var="k">
 				<object name="chart[k]Part" size="15 0 50%-10 100%-35">
@@ -190,7 +179,6 @@
 
 		<object type="button" name="continueButton" style="ModernButtonRed" size="100%-170 100%-52 100%-20 100%-15">
 			<translatableAttribute id="caption">Continue</translatableAttribute>
-			<action on="Press">continueButton();</action>
 		</object>
 	</object>
 </objects>
Index: source/gui/GUIManager.h
===================================================================
--- source/gui/GUIManager.h
+++ source/gui/GUIManager.h
@@ -72,12 +72,6 @@
 	 */
 	JS::Value PushPage(const std::wstring& pageName, Script::StructuredClone initData);
 
-	/**
-	 * Unload the currently active GUI page, and make the previous page active.
-	 * (There must be at least two pages when you call this.)
-	 */
-	void PopPage(Script::StructuredClone args);
-
 	/**
 	 * Called when a file has been modified, to hotload changes.
 	 */
@@ -151,21 +145,33 @@
 		 */
 		JS::Value ReplacePromise(ScriptInterface& scriptInterface);
 
+		struct CloseResult
+		{
+			Script::StructuredClone arg;
+			bool rejected;
+		};
+		CloseResult Close();
+
 		/**
 		 * Execute the stored callback function with the given arguments.
 		 */
-		void ResolvePromise(Script::StructuredClone args);
+		void Refocus(const CloseResult& result);
 
 		std::wstring m_Name;
 		std::unordered_set<VfsPath> inputs; // for hotloading
 		Script::StructuredClone initData; // data to be passed to the init() function
 		std::shared_ptr<CGUI> gui; // the actual GUI page
 
+		/**
+		 * When this promise is setteled this page should be closed.
+		 */
+		std::shared_ptr<JS::PersistentRootedObject> closePromise;
+
 		/**
 		 * Function executed by this parent GUI page when the child GUI page it pushed is popped.
 		 * Notice that storing it in the SGUIPage instead of CGUI means that it will survive the hotloading CGUI reset.
 		 */
-		std::shared_ptr<JS::PersistentRootedObject> callbackFunction;
+		std::shared_ptr<JS::PersistentRootedObject> childPromise;
 	};
 
 	std::shared_ptr<CGUI> top() const;
Index: source/gui/GUIManager.cpp
===================================================================
--- source/gui/GUIManager.cpp
+++ source/gui/GUIManager.cpp
@@ -141,26 +141,8 @@
 	return promise;
 }
 
-void CGUIManager::PopPage(Script::StructuredClone args)
-{
-	if (m_PageStack.size() < 2)
-	{
-		debug_warn(L"Tried to pop GUI page when there's < 2 in the stack");
-		return;
-	}
-
-	// Make sure we unfocus anything on the current page.
-	m_PageStack.back().gui->SendFocusMessage(GUIM_LOST_FOCUS);
-
-	m_PageStack.pop_back();
-	m_PageStack.back().ResolvePromise(args);
-
-	// We return to a page where some object might have been focused.
-	m_PageStack.back().gui->SendFocusMessage(GUIM_GOT_FOCUS);
-}
-
 CGUIManager::SGUIPage::SGUIPage(const CStrW& pageName, const Script::StructuredClone initData)
-	: m_Name(pageName), initData(initData), inputs(), gui(), callbackFunction()
+	: m_Name(pageName), initData(initData)
 {
 }
 
@@ -249,42 +231,78 @@
 	if (hotloadData)
 		Script::ReadStructuredClone(rq, hotloadData, &hotloadDataVal);
 
-	if (Script::HasProperty(rq, global, "init") &&
-	    !ScriptFunction::CallVoid(rq, global, "init", initDataVal, hotloadDataVal))
+	if (!Script::HasProperty(rq, global, "init"))
+	{
+		LOGERROR("GUI page '%s': There is no `init` function", utf8_from_wstring(m_Name));
+		return;
+	}
+
+	JS::RootedValue returnValue{rq.cx};
+	if (!ScriptFunction::Call(rq, global, "init", &returnValue, initDataVal, hotloadDataVal))
+	{
 		LOGERROR("GUI page '%s': Failed to call init() function", utf8_from_wstring(m_Name));
+		return;
+	}
+
+	if (!returnValue.isObject())
+	{
+		LOGERROR("GUI page '%s': `init` function didn't return an object.", utf8_from_wstring(m_Name));
+		return;
+	}
+
+	JS::RootedObject returnObject{rq.cx, &returnValue.toObject()};
+	if (!JS::IsPromiseObject(returnObject))
+	{
+		LOGERROR("GUI page '%s': `init` function didn't return a promise.", utf8_from_wstring(m_Name));
+		return;
+	}
+
+	closePromise = std::make_shared<JS::PersistentRootedObject>(rq.cx, returnObject);
 }
 
 JS::Value CGUIManager::SGUIPage::ReplacePromise(ScriptInterface& scriptInterface)
 {
 	JSContext* generalContext{scriptInterface.GetGeneralJSContext()};
-	callbackFunction =
+	childPromise =
 		std::make_shared<JS::PersistentRootedObject>(generalContext,
 			JS::NewPromiseObject(generalContext, nullptr));
 
-	return JS::ObjectValue(**callbackFunction);
+	return JS::ObjectValue(**childPromise);
 }
 
-void CGUIManager::SGUIPage::ResolvePromise(Script::StructuredClone args)
+CGUIManager::SGUIPage::CloseResult CGUIManager::SGUIPage::Close()
 {
-	if (!callbackFunction)
-		return;
+	// Make sure we unfocus anything on the current page.
+	gui->SendFocusMessage(GUIM_LOST_FOCUS);
+
+	ScriptRequest rq{gui->GetScriptInterface()};
+	JS::RootedValue arg{rq.cx, JS::GetPromiseResult(*closePromise)};
+	return {Script::WriteStructuredClone(rq, arg),
+		JS::GetPromiseState(*closePromise) == JS::PromiseState::Rejected};
+}
+
+void CGUIManager::SGUIPage::Refocus(const CloseResult& result)
+{
+	ENSURE(childPromise);
 
 	std::shared_ptr<ScriptInterface> scriptInterface = gui->GetScriptInterface();
 	ScriptRequest rq(scriptInterface);
 
 	JS::RootedObject globalObj(rq.cx, rq.glob);
 
-	JS::RootedObject funcVal{rq.cx, *callbackFunction};
+	JS::RootedObject funcVal{rq.cx, *childPromise};
 
 	// Delete the callback function, so that it is not called again
-	callbackFunction.reset();
+	childPromise.reset();
 
 	JS::RootedValue argVal(rq.cx);
-	if (args)
-		Script::ReadStructuredClone(rq, args, &argVal);
+	Script::ReadStructuredClone(rq, result.arg, &argVal);
 
 	// This only resolves the promise, it doesn't call the continuation.
-	JS::ResolvePromise(rq.cx, funcVal, argVal);
+	(result.rejected ? JS::RejectPromise : JS::ResolvePromise)(rq.cx, funcVal, argVal);
+
+	// We return to a page where some object might have been focused.
+	gui->SendFocusMessage(GUIM_GOT_FOCUS);
 }
 
 Status CGUIManager::ReloadChangedFile(const VfsPath& path)
@@ -374,6 +392,19 @@
 {
 	PROFILE3("gui tick");
 
+	while (!m_PageStack.empty() && m_PageStack.back().closePromise &&
+		JS::GetPromiseState(*m_PageStack.back().closePromise) != JS::PromiseState::Pending)
+	{
+		const size_t stackSize{m_PageStack.size()};
+		const SGUIPage::CloseResult result{m_PageStack.back().Close()};
+		ENSURE(m_PageStack.size() == stackSize);
+		m_PageStack.pop_back();
+		if (!m_PageStack.empty())
+			m_PageStack.back().Refocus(result);
+
+		g_ScriptContext->RunJobs();
+	}
+
 	// We share the script context with everything else that runs in the same thread.
 	// This call makes sure we trigger GC regularly even if the simulation is not running.
 	m_ScriptInterface->GetContext().MaybeIncrementalGC(1.0f);
@@ -383,6 +414,7 @@
 
 	for (const SGUIPage& p : pageStack)
 		p.gui->TickObjects();
+
 }
 
 void CGUIManager::Draw(CCanvas2D& canvas) const
Index: source/gui/Scripting/JSInterface_GUIManager.cpp
===================================================================
--- source/gui/Scripting/JSInterface_GUIManager.cpp
+++ source/gui/Scripting/JSInterface_GUIManager.cpp
@@ -43,17 +43,6 @@
 	g_GUI->SwitchPage(name, &scriptInterface, initData);
 }
 
-void PopGuiPage(const ScriptRequest& rq, JS::HandleValue args)
-{
-	if (g_GUI->GetPageCount() < 2)
-	{
-		ScriptException::Raise(rq, "Can't pop GUI pages when less than two pages are opened!");
-		return;
-	}
-
-	g_GUI->PopPage(Script::WriteStructuredClone(rq, args));
-}
-
 void SetCursor(const std::wstring& name)
 {
 	g_VideoMode.SetCursor(name);
@@ -79,7 +68,6 @@
 {
 	ScriptFunction::Register<&PushGuiPage>(rq, "PushGuiPage");
 	ScriptFunction::Register<&SwitchGuiPage>(rq, "SwitchGuiPage");
-	ScriptFunction::Register<&PopGuiPage>(rq, "PopGuiPage");
 	ScriptFunction::Register<&SetCursor>(rq, "SetCursor");
 	ScriptFunction::Register<&ResetCursor>(rq, "ResetCursor");
 	ScriptFunction::Register<&TemplateExists>(rq, "TemplateExists");
Index: source/gui/tests/test_GuiManager.h
===================================================================
--- source/gui/tests/test_GuiManager.h
+++ source/gui/tests/test_GuiManager.h
@@ -26,12 +26,14 @@
 #include "ps/GameSetup/GameSetup.h"
 #include "ps/Hotkey.h"
 #include "ps/XML/Xeromyces.h"
+#include "scriptinterface/FunctionWrapper.h"
 #include "scriptinterface/ScriptContext.h"
 #include "scriptinterface/ScriptRequest.h"
 #include "scriptinterface/ScriptInterface.h"
 #include "scriptinterface/StructuredClone.h"
 #include "scriptinterface/Object.h"
 
+#include "js/Promise.h"
 #include <memory>
 
 class TestGuiManager : public CxxTest::TestSuite
@@ -200,37 +202,70 @@
 		UnloadHotkeys();
 	}
 
-	void test_PageRegainedFocusEvent()
+	static void CloseTopmostPage()
 	{
-		// Load up a test page.
-		const ScriptInterface& scriptInterface = *(g_GUI->GetScriptInterface());
-		ScriptRequest rq(scriptInterface);
-		JS::RootedValue val(rq.cx);
-		Script::CreateObject(rq, &val);
+		ScriptRequest rq(g_GUI->GetActiveGUI()->GetScriptInterface());
+		JS::RootedValue global(rq.cx, rq.globalValue());
+		TS_ASSERT(ScriptFunction::CallVoid(rq, global, "closePage"));
 
-		TS_ASSERT_EQUALS(g_GUI->GetPageCount(), 0);
-		Script::StructuredClone data = Script::WriteStructuredClone(rq, JS::NullHandleValue);
-		g_GUI->PushPage(L"regainFocus/page_emptyPage.xml", data);
+		// Check if some promise are setteled also flush the promise-jobQueue.
+		g_GUI->TickObjects();
+	}
 
-		const ScriptInterface& pageScriptInterface = *(g_GUI->GetActiveGUI()->GetScriptInterface());
-		ScriptRequest prq(pageScriptInterface);
-		JS::RootedValue global(prq.cx, prq.globalValue());
+	void test_PageRegainedFocusEvent()
+	{
+		ScriptRequest rq{g_GUI->GetScriptInterface()};
+		Script::StructuredClone undefined{Script::WriteStructuredClone(rq, JS::UndefinedHandleValue)};
 
-		TS_ASSERT_EQUALS(g_GUI->GetPageCount(), 1);
-		g_GUI->PushPage(L"regainFocus/page_emptyPage.xml", data);
-		TS_ASSERT_EQUALS(g_GUI->GetPageCount(), 2);
-		g_GUI->PopPage(data);
+		TS_ASSERT_EQUALS(g_GUI->GetPageCount(), 0);
+		g_GUI->PushPage(L"regainFocus/page_emptyPage.xml", undefined);
 		TS_ASSERT_EQUALS(g_GUI->GetPageCount(), 1);
 
 		// This page instantly pushes an empty page with a callback that pops another page again.
-		g_GUI->PushPage(L"regainFocus/page_pushWithPopOnInit.xml", data);
+		g_GUI->PushPage(L"regainFocus/page_pushWithPopOnInit.xml", undefined);
 		TS_ASSERT_EQUALS(g_GUI->GetPageCount(), 3);
 
-		// Pop the empty page.
-		g_GUI->PopPage(data);
-		TS_ASSERT_EQUALS(g_GUI->GetPageCount(), 2);
-		// Execute the continuation.
-		scriptInterface.GetContext().RunJobs();
+		// Pop the empty page and execute the continuation.
+		CloseTopmostPage();
 		TS_ASSERT_EQUALS(g_GUI->GetPageCount(), 1);
+
+		CloseTopmostPage();
+		TS_ASSERT_EQUALS(g_GUI->GetPageCount(), 0);
+	}
+
+	void test_ResolveReject()
+	{
+		constexpr std::array<std::tuple<bool, JS::PromiseState>, 2> testSteps{{
+			{false, JS::PromiseState::Fulfilled},
+			{true, JS::PromiseState::Rejected}}};
+
+		const ScriptRequest rq{g_GUI->GetScriptInterface()};
+
+		const Script::StructuredClone undefined{
+			Script::WriteStructuredClone(rq, JS::UndefinedHandleValue)};
+		g_GUI->PushPage(L"regainFocus/page_emptyPage.xml", undefined);
+
+		for (const auto& [reject, result] : testSteps)
+		{
+			const JS::RootedValue value{rq.cx, JS::BooleanValue(reject)};
+			const Script::StructuredClone clonedValue{Script::WriteStructuredClone(rq, value)};
+
+			const JS::RootedValue promise{rq.cx,
+					g_GUI->PushPage(L"resolveReject/page_resolveReject.xml", clonedValue)};
+
+			// Check if some promise are setteled also flush the promise-jobQueue.
+			g_GUI->TickObjects();
+
+			const JS::RootedObject promiseObject{rq.cx, &promise.toObject()};
+			TS_ASSERT_EQUALS(JS::GetPromiseState(promiseObject), result);
+		}
+	}
+
+	void test_Sequential()
+	{
+		const ScriptRequest rq{g_GUI->GetScriptInterface()};
+		const Script::StructuredClone undefined{
+			Script::WriteStructuredClone(rq, JS::UndefinedHandleValue)};
+		g_GUI->PushPage(L"sequential/page_sequential.xml", undefined);
 	}
 };