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
@@ -1,50 +1,18 @@
-// We want to pass callback functions for the different buttons in a convenient way.
-// Because passing functions accross compartment boundaries is a pain, we just store them here together with some optional arguments.
-// The messageBox page will return the code of the pressed button and the according function will be called.
-var g_MessageBoxBtnFunctions = [];
-var g_MessageBoxCallbackArgs = [];
-
-function messageBoxCallbackFunction(btnCode)
-{
-	if (btnCode !== undefined && g_MessageBoxBtnFunctions[btnCode])
-	{
-		// Cache the variables to make it possible to call a messageBox from a callback function.
-		let callbackFunction = g_MessageBoxBtnFunctions[btnCode];
-		let callbackArgs = g_MessageBoxCallbackArgs[btnCode];
-
-		g_MessageBoxBtnFunctions = [];
-		g_MessageBoxCallbackArgs = [];
-
-		if (callbackArgs !== undefined)
-			callbackFunction(callbackArgs);
-		else
-			callbackFunction();
-		return;
-	}
-
-	g_MessageBoxBtnFunctions = [];
-	g_MessageBoxCallbackArgs = [];
-}
-
 function messageBox(mbWidth, mbHeight, mbMessage, mbTitle, mbButtonCaptions, mbBtnCode, mbCallbackArgs)
 {
-	if (g_MessageBoxBtnFunctions && g_MessageBoxBtnFunctions.length)
-	{
-		warn("A messagebox was called when a previous callback function is still set, aborting!");
-		return;
-	}
-
-	g_MessageBoxBtnFunctions = mbBtnCode;
-	g_MessageBoxCallbackArgs = mbCallbackArgs || g_MessageBoxCallbackArgs;
-
-	Engine.PushGuiPage("page_msgbox.xml", {
-		"width": mbWidth,
-		"height": mbHeight,
-		"message": mbMessage,
-		"title": mbTitle,
-		"buttonCaptions": mbButtonCaptions,
-		"callback": mbBtnCode && "messageBoxCallbackFunction"
-	});
+	Engine.PushGuiPage(
+		"page_msgbox.xml",
+		{
+			"width": mbWidth,
+			"height": mbHeight,
+			"message": mbMessage,
+			"title": mbTitle,
+			"buttonCaptions": mbButtonCaptions
+		},
+		btnCode => {
+			if (mbBtnCode !== undefined && mbBtnCode[btnCode])
+				mbBtnCode[btnCode](mbCallbackArgs ? mbCallbackArgs[btnCode] : undefined);
+		});
 }
 
 function openURL(url)
Index: binaries/data/mods/mod/gui/common/terms.js
===================================================================
--- binaries/data/mods/mod/gui/common/terms.js
+++ binaries/data/mods/mod/gui/common/terms.js
@@ -7,24 +7,29 @@
 
 function openTerms(page)
 {
-	Engine.PushGuiPage("page_termsdialog.xml", {
-		"file": g_Terms[page].file,
-		"title": g_Terms[page].title,
-		"sprintf": g_Terms[page].sprintf,
-		"urlButtons": g_Terms[page].urlButtons || [],
-		"termsURL": g_Terms[page].termsURL || undefined,
-		"page": page,
-		"callback": "acceptTerms"
-	});
-}
-
-function acceptTerms(data)
-{
-	g_Terms[data.page].accepted = data.accepted;
-	Engine.ConfigDB_CreateAndWriteValueToFile("user", g_Terms[data.page].config, data.accepted ? getTermsHash(data.page) : "0", "config/user.cfg");
-
-	if (g_Terms[data.page].callback)
-		g_Terms[data.page].callback(data);
+	Engine.PushGuiPage(
+		"page_termsdialog.xml",
+		{
+			"file": g_Terms[page].file,
+			"title": g_Terms[page].title,
+			"sprintf": g_Terms[page].sprintf,
+			"urlButtons": g_Terms[page].urlButtons || [],
+			"termsURL": g_Terms[page].termsURL || undefined,
+			"page": page
+		},
+		data => {
+			g_Terms[data.page].accepted = data.accepted;
+
+			Engine.ConfigDB_CreateAndWriteValueToFile(
+				"user",
+				g_Terms[data.page].config,
+				data.accepted ? getTermsHash(data.page) : "0",
+				"config/user.cfg");
+
+			if (g_Terms[data.page].callback)
+				g_Terms[data.page].callback(data);
+		}
+	);
 }
 
 function checkTerms()
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
@@ -268,9 +268,9 @@
 	hideDialog();
 }
 
-function closePage(data)
+function closePage()
 {
-	Engine.PopGuiPageCB(undefined);
+	Engine.PopGuiPage();
 }
 
 function showErrorMessageBox(caption, title, buttonCaptions, buttonActions)
Index: binaries/data/mods/mod/gui/modmod/modmodio.js
===================================================================
--- binaries/data/mods/mod/gui/modmod/modmodio.js
+++ binaries/data/mods/mod/gui/modmod/modmodio.js
@@ -26,7 +26,5 @@
 function openModIo(data)
 {
 	if (data.accepted)
-		Engine.PushGuiPage("page_modio.xml", {
-			"callback": "initMods"
-		});
+		Engine.PushGuiPage("page_modio.xml", {}, 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
@@ -28,22 +28,15 @@
 	let mbButton = [];
 	captions.forEach((caption, i) => {
 		mbButton[i] = Engine.GetGUIObjectByName("mbButton" + (i + 1));
-
-		let action = function()
-		{
-			if (data.callback)
-				Engine.PopGuiPageCB(i);
-			else
-				Engine.PopGuiPage();
-		};
-
 		mbButton[i].caption = caption;
-		mbButton[i].onPress = action;
 		mbButton[i].hidden = false;
+		mbButton[i].onPress = () => {
+			Engine.PopGuiPage(i);
+		};
 
 		// Convention: Cancel is the first button
 		if (i == 0)
-			mbCancelHotkey.onPress = action;
+			mbCancelHotkey.onPress = mbButton[i].onPress;
 	});
 
 	// Distribute buttons horizontally
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
@@ -82,7 +82,7 @@
 
 function closeTerms(accepted)
 {
-	Engine.PopGuiPageCB({
+	Engine.PopGuiPage({
 		"page": g_TermsPage,
 		"accepted": accepted
 	});
Index: binaries/data/mods/public/gui/aiconfig/aiconfig.js
===================================================================
--- binaries/data/mods/public/gui/aiconfig/aiconfig.js
+++ binaries/data/mods/public/gui/aiconfig/aiconfig.js
@@ -69,10 +69,7 @@
 function returnAI(save = true)
 {
 	let idx = Engine.GetGUIObjectByName("aiSelection").selected;
-
-	// Pop the page before calling the callback, so the callback runs
-	// in the parent GUI page's context
-	Engine.PopGuiPageCB({
+	Engine.PopGuiPage({
 		"save": save,
 		"id": g_AIDescriptions[idx].id,
 		"name": g_AIDescriptions[idx].data.name,
Index: binaries/data/mods/public/gui/civinfo/civinfo.js
===================================================================
--- binaries/data/mods/public/gui/civinfo/civinfo.js
+++ binaries/data/mods/public/gui/civinfo/civinfo.js
@@ -3,11 +3,6 @@
  */
 const g_CivData = loadCivData(true, false);
 
-/**
- * Callback function name on closing gui via Engine.PopGuiPage().
- */
-var g_Callback = "";
-
 var g_SelectedCiv = "";
 
 /**
@@ -15,9 +10,6 @@
  */
 function init(data = {})
 {
-	if (data.callback)
-		g_Callback = data.callback;
-
 	var civList = Object.keys(g_CivData).map(civ => ({ "name": g_CivData[civ].Name, "code": civ })).sort(sortNameIgnoreCase);
 	var civSelection = Engine.GetGUIObjectByName("civSelection");
 
@@ -94,16 +86,12 @@
 
 function switchToStrucTreePage()
 {
-	Engine.PopGuiPage();
-	Engine.PushGuiPage("page_structree.xml", { "civ": g_SelectedCiv, "callback": g_Callback });
+	Engine.PopGuiPage({ "civ": g_SelectedCiv, "nextPage": "page_structree.xml" });
 }
 
 function closePage()
 {
-	if (g_Callback)
-		Engine.PopGuiPageCB({ "civ": g_SelectedCiv, "page": "page_civinfo.xml" });
-	else
-		Engine.PopGuiPage();
+	Engine.PopGuiPage({ "civ": g_SelectedCiv, "page": "page_civinfo.xml" });
 }
 
 /**
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
@@ -22,7 +22,7 @@
  * Store civilization code and page (structree or history) opened in civilization info.
  */
 var g_CivInfo = {
-	"code": "",
+	"civ": "",
 	"page": "page_civinfo.xml"
 };
 
@@ -1047,10 +1047,10 @@
 				"hotkey_structree": colorizeHotkey("%(hotkey)s", "structree")
 			}),
 		"onPress": () => function() {
-			Engine.PushGuiPage(g_CivInfo.page, {
-				"civ": g_CivInfo.code,
-				"callback": "storeCivInfoPage"
-			});
+			Engine.PushGuiPage(
+				g_CivInfo.page,
+				{ "civ": g_CivInfo.civ },
+				storeCivInfoPage);
 		}
 	},
 	"civResetButton": {
@@ -2423,30 +2423,26 @@
 {
 	g_LastViewedAIPlayer = playerSlot;
 
-	Engine.PushGuiPage("page_aiconfig.xml", {
-		"callback": "AIConfigCallback",
-		"playerSlot": playerSlot,
-		"id": g_GameAttributes.settings.PlayerData[playerSlot].AI,
-		"difficulty": g_GameAttributes.settings.PlayerData[playerSlot].AIDiff,
-		"behavior": g_GameAttributes.settings.PlayerData[playerSlot].AIBehavior
-	});
-}
-
-/**
- * Called after closing the dialog.
- */
-function AIConfigCallback(ai)
-{
-	g_LastViewedAIPlayer = -1;
-
-	if (!ai.save || !g_IsController)
-		return;
-
-	g_GameAttributes.settings.PlayerData[ai.playerSlot].AI = ai.id;
-	g_GameAttributes.settings.PlayerData[ai.playerSlot].AIDiff = ai.difficulty;
-	g_GameAttributes.settings.PlayerData[ai.playerSlot].AIBehavior = ai.behavior;
+	Engine.PushGuiPage(
+		"page_aiconfig.xml",
+		{
+			"playerSlot": playerSlot,
+			"id": g_GameAttributes.settings.PlayerData[playerSlot].AI,
+			"difficulty": g_GameAttributes.settings.PlayerData[playerSlot].AIDiff,
+			"behavior": g_GameAttributes.settings.PlayerData[playerSlot].AIBehavior
+		},
+		ai => {
+			g_LastViewedAIPlayer = -1;
+
+			if (!ai.save || !g_IsController)
+				return;
+
+			g_GameAttributes.settings.PlayerData[ai.playerSlot].AI = ai.id;
+			g_GameAttributes.settings.PlayerData[ai.playerSlot].AIDiff = ai.difficulty;
+			g_GameAttributes.settings.PlayerData[ai.playerSlot].AIBehavior = ai.behavior;
 
-	updateGameAttributes();
+			updateGameAttributes();
+		});
 }
 
 function reloadPlayerAssignmentChoices()
@@ -2775,6 +2771,11 @@
 
 function storeCivInfoPage(data)
 {
-	g_CivInfo.code = data.civ;
-	g_CivInfo.page = data.page;
+	if (data.nextPage)
+		Engine.PushGuiPage(
+			data.nextPage,
+			{ "civ": data.civ },
+			storeCivInfoPage);
+	else
+		g_CivInfo = data;
 }
Index: binaries/data/mods/public/gui/gamesetup/gamesetup.xml
===================================================================
--- binaries/data/mods/public/gui/gamesetup/gamesetup.xml
+++ binaries/data/mods/public/gui/gamesetup/gamesetup.xml
@@ -6,15 +6,11 @@
 	<script directory="gui/gamesetup/"/>
 
 	<object	hotkey="civinfo">
-		<action on="Press">
-			Engine.PushGuiPage("page_civinfo.xml", { "civ": g_CivInfo.code, "callback": "storeCivInfoPage" });
-		</action>
+		<action on="Press">Engine.PushGuiPage("page_civinfo.xml", { "civ": g_CivInfo.civ }, storeCivInfoPage);</action>
 	</object>
 
 	<object	hotkey="structree">
-		<action on="Press">
-			Engine.PushGuiPage("page_structree.xml", { "civ": g_CivInfo.code, "callback": "storeCivInfoPage" });
-		</action>
+		<action on="Press">Engine.PushGuiPage("page_structree.xml", { "civ": g_CivInfo.civ }, storeCivInfoPage);</action>
 	</object>
 
 	<object hotkey="cancel">
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
@@ -55,7 +55,7 @@
 function openAdvancedMenu()
 {
 	let localeText = Engine.GetGUIObjectByName("localeText");
-	Engine.PushGuiPage("page_locale_advanced.xml", { "callback": "applyFromAdvancedMenu", "locale": localeText.caption });
+	Engine.PushGuiPage("page_locale_advanced.xml", { "locale": localeText.caption }, applyFromAdvancedMenu);
 }
 
 function applyFromAdvancedMenu(locale)
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
@@ -114,5 +114,5 @@
 function applySelectedLocale()
 {
 	var resultingLocaleText = Engine.GetGUIObjectByName("resultingLocale");
-	Engine.PopGuiPageCB(resultingLocaleText.caption);
+	Engine.PopGuiPage(resultingLocaleText.caption);
 }
Index: binaries/data/mods/public/gui/manual/manual.js
===================================================================
--- binaries/data/mods/public/gui/manual/manual.js
+++ /dev/null
@@ -1,15 +0,0 @@
-var hasCallback = false;
-
-function init(data)
-{
-	Engine.GetGUIObjectByName("mainText").caption = Engine.TranslateLines(Engine.ReadFile("gui/manual/intro.txt"));
-	hasCallback = data && data.callback;
-}
-
-function closeManual()
-{
-	if (hasCallback)
-		Engine.PopGuiPageCB();
-	else
-		Engine.PopGuiPage();
-}
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
@@ -14,13 +14,16 @@
 		</object>
 
 		<object type="image" sprite="ModernFade" size="20 20 100%-20 100%-58">
-			<object name="mainText" type="text" style="ModernTextPanel"/>
+			<object name="mainText" type="text" style="ModernTextPanel">
+				<action on="Load">this.caption = Engine.TranslateLines(Engine.ReadFile("gui/manual/intro.txt"));</action>
+			</object>
 		</object>
 
 		<object 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">closeManual();</action>
+			<action on="Press">Engine.PopGuiPage();</action>
 		</object>
+
 		<object name="url" type="button" style="ModernButtonRed" size="100%-214 100%-52 100%-24 100%-24">
 			<translatableAttribute id="caption">View Online</translatableAttribute>
 			<action on="Press">openURL("https://trac.wildfiregames.com/wiki/0adManual");</action>
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
@@ -4,12 +4,7 @@
 var g_Options;
 
 /**
- * Remember whether to unpause running singleplayer games.
- */
-var g_HasCallback;
-
-/**
- * Functions to call after closing the page.
+ * Names of session functions to be called after closing the page.
  */
 var g_CloseCallbacks;
 
@@ -170,8 +165,7 @@
 
 function init(data, hotloadData)
 {
-	g_CloseCallbacks = new Set();
-	g_HasCallback = hotloadData && hotloadData.callback || data && data.callback;
+	g_CloseCallbacks = hotloadData ? hotloadData.closeCallbacks : new Set();
 	g_TabCategorySelected = hotloadData ? hotloadData.tabCategorySelected : 0;
 
 	g_Options = Engine.ReadJSONFile("gui/options/options.json");
@@ -190,7 +184,7 @@
 {
 	return {
 		"tabCategorySelected": g_TabCategorySelected,
-		"callback": g_HasCallback
+		"closeCallbacks": g_CloseCallbacks
 	};
 }
 
@@ -382,8 +376,5 @@
 
 function closePageWithoutConfirmation()
 {
-	if (g_HasCallback)
-		Engine.PopGuiPageCB(g_CloseCallbacks);
-	else
-		Engine.PopGuiPage();
+	Engine.PopGuiPage(g_CloseCallbacks);
 }
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
@@ -105,9 +105,7 @@
 
 function ShowSplashScreen()
 {
-	Engine.PushGuiPage("page_splashscreen.xml", {
-		"callback": "ShowRenderPathMessage"
-	});
+	Engine.PushGuiPage("page_splashscreen.xml", {}, ShowRenderPathMessage);
 }
 
 function ShowRenderPathMessage()
@@ -232,3 +230,15 @@
 {
 	return translate("Launch the multiplayer lobby to join and host publicly visible games and chat with other players. \\[DISABLED BY BUILD]");
 }
+
+function openStrucTree(page)
+{
+	closeMenu();
+	Engine.PushGuiPage(page, {}, storeCivInfoPage);
+}
+
+function storeCivInfoPage(data)
+{
+	if (data.nextPage)
+		Engine.PushGuiPage(data.nextPage, { "civ": data.civ }, storeCivInfoPage);
+}
Index: binaries/data/mods/public/gui/pregame/mainmenu.xml
===================================================================
--- binaries/data/mods/public/gui/pregame/mainmenu.xml
+++ binaries/data/mods/public/gui/pregame/mainmenu.xml
@@ -118,10 +118,7 @@
 					hotkey="structree"
 				>
 					<translatableAttribute id="caption">Structure Tree</translatableAttribute>
-					<action on="Press">
-						closeMenu();
-						Engine.PushGuiPage("page_structree.xml", {});
-					</action>
+					<action on="Press">openStrucTree("page_structree.xml");</action>
 				</object>
 
 				<!-- HISTORY BUTTON -->
@@ -134,10 +131,7 @@
 					hotkey="civinfo"
 				>
 					<translatableAttribute id="caption">History</translatableAttribute>
-					<action on="Press">
-						closeMenu();
-						Engine.PushGuiPage("page_civinfo.xml");
-					</action>
+					<action on="Press">openStrucTree("page_civinfo.xml");</action>
 				</object>
 
 			</object>
Index: binaries/data/mods/public/gui/reference/common/core.js
===================================================================
--- binaries/data/mods/public/gui/reference/common/core.js
+++ binaries/data/mods/public/gui/reference/common/core.js
@@ -1,13 +1,4 @@
 var g_SelectedCiv = "gaia";
-var g_CallbackSet = false;
-
-function closePage()
-{
-	if (g_CallbackSet)
-		Engine.PopGuiPageCB(0);
-	else
-		Engine.PopGuiPage();
-}
 
 /**
  * Compile lists of templates buildable/trainable/researchable of a given civ.
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
@@ -9,20 +9,12 @@
 var g_TrainList = {};
 
 /**
- * Callback function name on closing gui via Engine.PopGuiPage().
- */
-var g_Callback = "";
-
-/**
  * Initialize the page
  *
  * @param {object} data - Parameters passed from the code that calls this page into existence.
  */
 function init(data = {})
 {
-	if (data.callback)
-		g_Callback = data.callback;
-
 	let civList = Object.keys(g_CivData).map(civ => ({
 		"name": g_CivData[civ].Name,
 		"code": civ,
@@ -52,16 +44,12 @@
 
 function switchToCivInfoPage()
 {
-	Engine.PopGuiPage();
-	Engine.PushGuiPage("page_civinfo.xml", { "civ": g_SelectedCiv, "callback": g_Callback });
+	Engine.PopGuiPage({ "civ": g_SelectedCiv, "nextPage": "page_civinfo.xml" });
 }
 
 function closePage()
 {
-	if (g_Callback)
-		Engine.PopGuiPageCB({ "civ": g_SelectedCiv, "page": "page_structree.xml" });
-	else
-		Engine.PopGuiPage();
+	Engine.PopGuiPage({ "civ": g_SelectedCiv, "page": "page_structree.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
@@ -47,9 +47,6 @@
  * @param {object} data - Contains the civCode and the name of the template to display.
  * @param {string} data.templateName
  * @param {string} [data.civ]
- * @param {*} [data.callback] - If set and loosely equivalent to true, a callback is
- *                              assumed to be setup ready be called by the Engine upon
- *                              closure of this page.
  */
 function init(data)
 {
@@ -60,9 +57,6 @@
 		return;
 	}
 
-	if (data.callback)
-		g_CallbackSet = true;
-
 	let templateName = removeFiltersFromTemplateName(data.templateName);
 	let isTech = techDataExists(templateName);
 
Index: binaries/data/mods/public/gui/reference/viewer/viewer.xml
===================================================================
--- binaries/data/mods/public/gui/reference/viewer/viewer.xml
+++ binaries/data/mods/public/gui/reference/viewer/viewer.xml
@@ -35,7 +35,7 @@
 			hotkey="cancel"
 		>
 			<translatableAttribute id="caption">Close</translatableAttribute>
-			<action on="Press">closePage();</action>
+			<action on="Press">Engine.PopGuiPage();</action>
 		</object>
 	</object>
 
Index: binaries/data/mods/public/gui/savegame/save.js
===================================================================
--- binaries/data/mods/public/gui/savegame/save.js
+++ binaries/data/mods/public/gui/savegame/save.js
@@ -80,7 +80,7 @@
 
 function closeSave()
 {
-	Engine.PopGuiPageCB(0);
+	Engine.PopGuiPage();
 }
 
 // HACK: Engine.SaveGame* expects this function to be defined on the current page.
Index: binaries/data/mods/public/gui/session/hotkeys/misc.xml
===================================================================
--- binaries/data/mods/public/gui/session/hotkeys/misc.xml
+++ binaries/data/mods/public/gui/session/hotkeys/misc.xml
@@ -33,15 +33,11 @@
 	</object>
 
 	<object	hotkey="civinfo">
-		<action on="Press">
-			Engine.PushGuiPage("page_civinfo.xml", { "civ": g_CivInfo.code, "callback": "storeCivInfoPage" });
-		</action>
+		<action on="Press">openStrucTree("page_civinfo.xml");</action>
 	</object>
 
 	<object	hotkey="structree">
-		<action on="Press">
-			Engine.PushGuiPage("page_structree.xml", { "civ": g_CivInfo.code, "callback": "storeCivInfoPage" });
-		</action>
+		<action on="Press">openStrucTree("page_structree.xml");</action>
 	</object>
 
 	<object hotkey="silhouettes">
Index: binaries/data/mods/public/gui/session/menu.js
===================================================================
--- binaries/data/mods/public/gui/session/menu.js
+++ binaries/data/mods/public/gui/session/menu.js
@@ -29,7 +29,7 @@
  * Store civilization code and page (structree or history) opened in civilization info.
  */
 var g_CivInfo = {
-	"code": "",
+	"civ": "",
 	"page": "page_structree.xml"
 };
 
@@ -225,10 +225,10 @@
 	closeOpenDialogs();
 	pauseGame();
 
-	Engine.PushGuiPage("page_savegame.xml", {
-		"savedGameData": getSavedGameData(),
-		"callback": "resumeGame"
-	});
+	Engine.PushGuiPage(
+		"page_savegame.xml",
+		{ "savedGameData": getSavedGameData() },
+		resumeGame);
 }
 
 function openOptions()
@@ -236,18 +236,16 @@
 	closeOpenDialogs();
 	pauseGame();
 
-	Engine.PushGuiPage("page_options.xml", {
-		"callback": "optionsPageClosed"
-	});
-}
-
-function optionsPageClosed(data)
-{
-	for (let callback of data)
-		if (global[callback])
-			global[callback]();
+	Engine.PushGuiPage(
+		"page_options.xml",
+		{},
+		callbackFunctionNames => {
+			for (let functionName of callbackFunctionNames)
+				if (global[functionName])
+					global[functionName]();
 
-	resumeGame();
+			resumeGame();
+		});
 }
 
 function openChat(command = "")
@@ -1090,41 +1088,51 @@
 	pauseGame();
 
 	let extendedSimState = Engine.GuiInterfaceCall("GetExtendedSimulationState");
-	Engine.PushGuiPage("page_summary.xml", {
-		"sim": {
-			"mapSettings": g_GameAttributes.settings,
-			"playerStates": extendedSimState.players.filter((state, player) =>
-				g_IsObserver || player == 0 || player == g_ViewedPlayer ||
-				extendedSimState.players[g_ViewedPlayer].hasSharedLos && g_Players[player].isMutualAlly[g_ViewedPlayer]),
-			"timeElapsed": extendedSimState.timeElapsed
-		},
-		"gui": {
-			"dialog": true,
-			"isInGame": true
+	Engine.PushGuiPage(
+		"page_summary.xml",
+		{
+			"sim": {
+				"mapSettings": g_GameAttributes.settings,
+				"playerStates": extendedSimState.players.filter((state, player) =>
+					g_IsObserver || player == 0 || player == g_ViewedPlayer ||
+					extendedSimState.players[g_ViewedPlayer].hasSharedLos && g_Players[player].isMutualAlly[g_ViewedPlayer]),
+				"timeElapsed": extendedSimState.timeElapsed
+			},
+			"gui": {
+				"dialog": true,
+				"isInGame": true
+			},
+			"selectedData": g_SummarySelectedData
 		},
-		"selectedData": g_SummarySelectedData,
-		"callback": "resumeGameAndSaveSummarySelectedData"
-	});
+		resumeGameAndSaveSummarySelectedData);
 }
 
-function openStrucTree()
+function openStrucTree(page)
 {
 	closeOpenDialogs();
 	pauseGame();
 
-	// TODO add info about researched techs and unlocked entities
-
-	Engine.PushGuiPage(g_CivInfo.page, {
-		"civ": g_CivInfo.code || g_Players[g_ViewedPlayer].civ,
-		"callback": "storeCivInfoPage"
-	});
+	Engine.PushGuiPage(
+		page,
+		{
+			"civ": g_CivInfo.civ || g_Players[g_ViewedPlayer].civ
+			// TODO add info about researched techs and unlocked entities
+		},
+		storeCivInfoPage);
 }
 
 function storeCivInfoPage(data)
 {
-	g_CivInfo.code = data.civ;
-	g_CivInfo.page = data.page;
-	resumeGame();
+	if (data.nextPage)
+		Engine.PushGuiPage(
+			data.nextPage,
+			{ "civ": data.civ },
+			storeCivInfoPage);
+	else
+	{
+		g_CivInfo = data;
+		resumeGame();
+	}
 }
 
 /**
Index: binaries/data/mods/public/gui/session/selection_panels.js
===================================================================
--- binaries/data/mods/public/gui/session/selection_panels.js
+++ binaries/data/mods/public/gui/session/selection_panels.js
@@ -1143,11 +1143,13 @@
 {
 	pauseGame();
 
-	Engine.PushGuiPage("page_viewer.xml", {
-		"templateName": templateName,
-		"callback": "resumeGame",
-		"civ": civCode
-	});
+	Engine.PushGuiPage(
+		"page_viewer.xml",
+		{
+			"templateName": templateName,
+			"civ": civCode
+		},
+		resumeGame);
 }
 
 /**
Index: binaries/data/mods/public/gui/session/top_panel/civ_icon.xml
===================================================================
--- binaries/data/mods/public/gui/session/top_panel/civ_icon.xml
+++ binaries/data/mods/public/gui/session/top_panel/civ_icon.xml
@@ -6,6 +6,6 @@
 	tooltip_style="sessionToolTipBold"
 >
 	<object name="civIconOverlay" style="CivIconOverlay" size="0 0 100% 100%" type="button">
-		<action on="Press">openStrucTree()</action>
+		<action on="Press">openStrucTree(g_CivInfo.page)</action>
 	</object>
 </object>
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
@@ -10,5 +10,5 @@
 {
 	Engine.ConfigDB_CreateAndWriteValueToFile("user", "gui.splashscreen.enable", String(Engine.GetGUIObjectByName("displaySplashScreen").checked), "config/user.cfg");
 	Engine.ConfigDB_CreateAndWriteValueToFile("user", "gui.splashscreen.version", Engine.GetFileMTime(g_SplashScreenFile), "config/user.cfg");
-	Engine.PopGuiPageCB();
+	Engine.PopGuiPage();
 }
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
@@ -443,7 +443,7 @@
 		"charts": g_SelectedChart
 	};
 	if (g_GameData.gui.isInGame)
-		Engine.PopGuiPageCB({
+		Engine.PopGuiPage({
 			"explicitResume": 0,
 			"summarySelectedData": summarySelectedData
 		});
Index: source/gui/GUIManager.h
===================================================================
--- source/gui/GUIManager.h
+++ source/gui/GUIManager.h
@@ -72,15 +72,15 @@
 	 * Load a new GUI page and make it active. All current pages will be retained,
 	 * and will still be drawn and receive tick events, but will not receive
 	 * user inputs.
+	 * If given, the callbackHandler function will be executed once this page is closed.
 	 */
-	void PushPage(const CStrW& pageName, shared_ptr<ScriptInterface::StructuredClone> initData);
+	void PushPage(const CStrW& pageName, shared_ptr<ScriptInterface::StructuredClone> initData, JS::HandleValue callbackFunc);
 
 	/**
 	 * 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();
-	void PopPageCB(shared_ptr<ScriptInterface::StructuredClone> args);
+	void PopPage(shared_ptr<ScriptInterface::StructuredClone> args);
 
 	/**
 	 * Called when a file has been modified, to hotload changes.
@@ -145,13 +145,26 @@
 	{
 		// COPYABLE, because event handlers may invalidate page stack iterators by open or close pages,
 		// and event handlers need to be called for the entire stack.
+
 		SGUIPage(const CStrW& pageName, const shared_ptr<ScriptInterface::StructuredClone> initData);
+
 		void LoadPage(shared_ptr<ScriptRuntime> scriptRuntime);
 
+		void SetCallbackFunction(ScriptInterface& scriptInterface, JS::HandleValue callbackFunc);
+
+		void PerformCallbackFunction(shared_ptr<ScriptInterface::StructuredClone> args);
+
 		CStrW name;
 		boost::unordered_set<VfsPath> inputs; // for hotloading
 		shared_ptr<ScriptInterface::StructuredClone> initData; // data to be passed to the init() function
 		shared_ptr<CGUI> gui; // the actual GUI page
+
+	private:
+		/**
+		 * 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.
+		 */
+		shared_ptr<JS::PersistentRootedValue> callbackFunction;
 	};
 
 	shared_ptr<CGUI> top() const;
Index: source/gui/GUIManager.cpp
===================================================================
--- source/gui/GUIManager.cpp
+++ source/gui/GUIManager.cpp
@@ -89,19 +89,24 @@
 
 	m_PageStack.clear();
 
-	PushPage(pageName, initDataClone);
+	PushPage(pageName, initDataClone, JS::UndefinedHandleValue);
 }
 
-void CGUIManager::PushPage(const CStrW& pageName, shared_ptr<ScriptInterface::StructuredClone> initData)
+void CGUIManager::PushPage(const CStrW& pageName, shared_ptr<ScriptInterface::StructuredClone> initData, JS::HandleValue callbackFunction)
 {
+	// Store the callback handler in the current GUI page before opening the new one
+	if (!m_PageStack.empty() && !callbackFunction.isUndefined())
+		m_PageStack.back().SetCallbackFunction(*m_ScriptInterface, callbackFunction);
+
 	// Push the page prior to loading its contents, because that may push
 	// another GUI page on init which should be pushed on top of this new page.
 	m_PageStack.emplace_back(pageName, initData);
 	m_PageStack.back().LoadPage(m_ScriptRuntime);
+
 	ResetCursor();
 }
 
-void CGUIManager::PopPage()
+void CGUIManager::PopPage(shared_ptr<ScriptInterface::StructuredClone> args)
 {
 	if (m_PageStack.size() < 2)
 	{
@@ -110,58 +115,11 @@
 	}
 
 	m_PageStack.pop_back();
-}
-
-void CGUIManager::PopPageCB(shared_ptr<ScriptInterface::StructuredClone> args)
-{
-	shared_ptr<ScriptInterface::StructuredClone> initDataClone = m_PageStack.back().initData;
-	PopPage();
-
-	shared_ptr<ScriptInterface> scriptInterface = m_PageStack.back().gui->GetScriptInterface();
-	JSContext* cx = scriptInterface->GetContext();
-	JSAutoRequest rq(cx);
-
-	JS::RootedValue initDataVal(cx);
-	if (!initDataClone)
-	{
-		LOGERROR("Called PopPageCB when initData (which should contain the callback function name) isn't set!");
-		return;
-	}
-
-	scriptInterface->ReadStructuredClone(initDataClone, &initDataVal);
-
-	if (!scriptInterface->HasProperty(initDataVal, "callback"))
-	{
-		LOGERROR("Called PopPageCB when the callback function name isn't set!");
-		return;
-	}
-
-	std::string callback;
-	if (!scriptInterface->GetProperty(initDataVal, "callback", callback))
-	{
-		LOGERROR("Failed to get the callback property as a string from initData in PopPageCB!");
-		return;
-	}
-
-	JS::RootedValue global(cx, scriptInterface->GetGlobalObject());
-	if (!scriptInterface->HasProperty(global, callback.c_str()))
-	{
-		LOGERROR("The specified callback function %s does not exist in the page %s", callback, utf8_from_wstring(m_PageStack.back().name));
-		return;
-	}
-
-	JS::RootedValue argVal(cx);
-	if (args)
-		scriptInterface->ReadStructuredClone(args, &argVal);
-	if (!scriptInterface->CallFunctionVoid(global, callback.c_str(), argVal))
-	{
-		LOGERROR("Failed to call the callback function %s in the page %s", callback, utf8_from_wstring(m_PageStack.back().name));
-		return;
-	}
+	m_PageStack.back().PerformCallbackFunction(args);
 }
 
 CGUIManager::SGUIPage::SGUIPage(const CStrW& pageName, const shared_ptr<ScriptInterface::StructuredClone> initData)
-	: name(pageName), initData(initData), inputs(), gui()
+	: name(pageName), initData(initData), inputs(), gui(), callbackFunction()
 {
 }
 
@@ -256,6 +214,52 @@
 		LOGERROR("GUI page '%s': Failed to call init() function", utf8_from_wstring(name));
 }
 
+void CGUIManager::SGUIPage::SetCallbackFunction(ScriptInterface& scriptInterface, JS::HandleValue callbackFunc)
+{
+	if (!callbackFunc.isObject())
+	{
+		LOGERROR("Given callback handler is not an object!");
+		return;
+	}
+
+	// Does not require JSAutoRequest
+	if (!JS_ObjectIsFunction(scriptInterface.GetContext(), &callbackFunc.toObject()))
+	{
+		LOGERROR("Given callback handler is not a function!");
+		return;
+	}
+
+	callbackFunction = std::make_shared<JS::PersistentRootedValue>(scriptInterface.GetJSRuntime(), callbackFunc);
+}
+
+void CGUIManager::SGUIPage::PerformCallbackFunction(shared_ptr<ScriptInterface::StructuredClone> args)
+{
+	if (!callbackFunction)
+		return;
+
+	shared_ptr<ScriptInterface> scriptInterface = gui->GetScriptInterface();
+	JSContext* cx = scriptInterface->GetContext();
+	JSAutoRequest rq(cx);
+
+	JS::RootedObject globalObj(cx, &scriptInterface->GetGlobalObject().toObject());
+
+	JS::RootedValue funcVal(cx, *callbackFunction);
+
+	// Delete the callback function, so that it is not called again
+	callbackFunction.reset();
+
+	JS::RootedValue argVal(cx);
+	if (args)
+		scriptInterface->ReadStructuredClone(args, &argVal);
+
+	JS::AutoValueVector paramData(cx);
+	paramData.append(argVal);
+
+	JS::RootedValue result(cx);
+
+	JS_CallFunctionValue(cx, globalObj, funcVal, paramData, &result);
+}
+
 Status CGUIManager::ReloadChangedFile(const VfsPath& path)
 {
 	for (SGUIPage& p : m_PageStack)
Index: source/gui/scripting/JSInterface_GUIManager.h
===================================================================
--- source/gui/scripting/JSInterface_GUIManager.h
+++ source/gui/scripting/JSInterface_GUIManager.h
@@ -23,10 +23,9 @@
 
 namespace JSI_GUIManager
 {
-	void PushGuiPage(ScriptInterface::CxPrivate* pCxPrivate, const std::wstring& name, JS::HandleValue initData);
+	void PushGuiPage(ScriptInterface::CxPrivate* pCxPrivate, const std::wstring& name, JS::HandleValue initData, JS::HandleValue callbackFunction);
 	void SwitchGuiPage(ScriptInterface::CxPrivate* pCxPrivate, const std::wstring& name, JS::HandleValue initData);
-	void PopGuiPage(ScriptInterface::CxPrivate* pCxPrivate);
-	void PopGuiPageCB(ScriptInterface::CxPrivate* pCxPrivate, JS::HandleValue args);
+	void PopGuiPage(ScriptInterface::CxPrivate* pCxPrivate, JS::HandleValue args);
 	JS::Value GetGUIObjectByName(ScriptInterface::CxPrivate* pCxPrivate, const std::string& name);
 	std::wstring SetCursor(ScriptInterface::CxPrivate* pCxPrivate, const std::wstring& name);
 	void ResetCursor(ScriptInterface::CxPrivate* pCxPrivate);
Index: source/gui/scripting/JSInterface_GUIManager.cpp
===================================================================
--- source/gui/scripting/JSInterface_GUIManager.cpp
+++ source/gui/scripting/JSInterface_GUIManager.cpp
@@ -1,4 +1,4 @@
-/* Copyright (C) 2018 Wildfire Games.
+/* Copyright (C) 2019 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -25,11 +25,9 @@
 #include "ps/GameSetup/Config.h"
 #include "scriptinterface/ScriptInterface.h"
 
-// Note that the initData argument may only contain clonable data.
-// Functions aren't supported for example!
-void JSI_GUIManager::PushGuiPage(ScriptInterface::CxPrivate* pCxPrivate, const std::wstring& name, JS::HandleValue initData)
+void JSI_GUIManager::PushGuiPage(ScriptInterface::CxPrivate* pCxPrivate, const std::wstring& name, JS::HandleValue initData, JS::HandleValue callbackFunction)
 {
-	g_GUI->PushPage(name, pCxPrivate->pScriptInterface->WriteStructuredClone(initData));
+	g_GUI->PushPage(name, pCxPrivate->pScriptInterface->WriteStructuredClone(initData), callbackFunction);
 }
 
 void JSI_GUIManager::SwitchGuiPage(ScriptInterface::CxPrivate* pCxPrivate, const std::wstring& name, JS::HandleValue initData)
@@ -37,14 +35,9 @@
 	g_GUI->SwitchPage(name, pCxPrivate->pScriptInterface, initData);
 }
 
-void JSI_GUIManager::PopGuiPage(ScriptInterface::CxPrivate* UNUSED(pCxPrivate))
+void JSI_GUIManager::PopGuiPage(ScriptInterface::CxPrivate* pCxPrivate, JS::HandleValue args)
 {
-	g_GUI->PopPage();
-}
-
-void JSI_GUIManager::PopGuiPageCB(ScriptInterface::CxPrivate* pCxPrivate, JS::HandleValue args)
-{
-	g_GUI->PopPageCB(pCxPrivate->pScriptInterface->WriteStructuredClone(args));
+	g_GUI->PopPage(pCxPrivate->pScriptInterface->WriteStructuredClone(args));
 }
 
 JS::Value JSI_GUIManager::GetGUIObjectByName(ScriptInterface::CxPrivate* pCxPrivate, const std::string& name)
@@ -82,10 +75,9 @@
 
 void JSI_GUIManager::RegisterScriptFunctions(const ScriptInterface& scriptInterface)
 {
-	scriptInterface.RegisterFunction<void, std::wstring, JS::HandleValue, &PushGuiPage>("PushGuiPage");
+	scriptInterface.RegisterFunction<void, std::wstring, JS::HandleValue, JS::HandleValue, &PushGuiPage>("PushGuiPage");
 	scriptInterface.RegisterFunction<void, std::wstring, JS::HandleValue, &SwitchGuiPage>("SwitchGuiPage");
-	scriptInterface.RegisterFunction<void, &PopGuiPage>("PopGuiPage");
-	scriptInterface.RegisterFunction<void, JS::HandleValue, &PopGuiPageCB>("PopGuiPageCB");
+	scriptInterface.RegisterFunction<void, JS::HandleValue, &PopGuiPage>("PopGuiPage");
 	scriptInterface.RegisterFunction<JS::Value, std::string, &GetGUIObjectByName>("GetGUIObjectByName");
 	scriptInterface.RegisterFunction<std::wstring, std::wstring, &SetCursor>("SetCursor");
 	scriptInterface.RegisterFunction<void, &ResetCursor>("ResetCursor");