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
@@ -7,7 +7,7 @@
 		g_HasCallback = true;
 	g_Controls = {};
 
-	var options = Engine.ReadJSONFile("gui/options/options.json");
+	let options = Engine.ReadJSONFile("gui/options/options.json");
 	for (let category in options)
 	{
 		let lastSize;
@@ -67,14 +67,14 @@
  */
 function setupControl(option, i, category)
 {
-	var control;
-	var onUpdate;
-	var key = option.parameters.config;
+	let control;
+	let key = option.parameters.config;
 
 	switch (option.type)
 	{
 	case "boolean":
 	case "invertedboolean":
+	{
 		// More space for the label
 		let text = Engine.GetGUIObjectByName(category + "Label[" + i + "]");
 		let size = text.size;
@@ -110,11 +110,14 @@
 			}
 		}
 		// invertedboolean when we want to display the opposite of the flag value
-		var inverted = option.type === "invertedboolean";
+		let inverted = option.type === "invertedboolean";
 		if (inverted)
 			checked = !checked;
 
-		onUpdate = function(key, keyRenderer, inverted)
+		// Load final data to the control element.
+		control.checked = checked;
+
+		control.onPress = function(key, keyRenderer, inverted)
 		{
 			return function()
 			{
@@ -126,12 +129,10 @@
 				updateOptionPanel();
 			};
 		}(key, keyRenderer, inverted);
-
-		// Load final data to the control element.
-		control.checked = checked;
-		control.onPress = onUpdate;
 		break;
+	}
 	case "slider":
+	{
 		control = Engine.GetGUIObjectByName(category + "Slider[" + i + "]");
 		let value;
 		let callbackFunction;
@@ -160,7 +161,7 @@
 			}
 		}
 
-		onUpdate = function(key, callbackFunction, minvalue, maxvalue)
+		control.onSelectionChange = function(key, callbackFunction, minvalue, maxvalue)
 		{
 			return function()
 			{
@@ -178,10 +179,11 @@
 		control.value = value;
 		control.max_value = maxvalue;
 		control.min_value = minvalue;
-		control.onValueChange = onUpdate;
 		break;
+	}
 	case "number":
 	case "string":
+	{
 		control = Engine.GetGUIObjectByName(category + "Input[" + i + "]");
 		let caption;
 		let functionBody;
@@ -214,7 +216,7 @@
 		// - when the mouse leave the control (MouseLeave event)
 		// - or when saving or closing the window (registerChanges function)
 		// so we must ensure that something has indeed been modified
-		onUpdate = function(key, functionBody, minval, maxval)
+		let onUpdate = function(key, functionBody, minval, maxval)
 		{
 			return function()
 			{
@@ -236,7 +238,9 @@
 		control.onPress = onUpdate;
 		control.onMouseLeave = onUpdate;
 		break;
+	}
 	case "dropdown":
+	{
 		control = Engine.GetGUIObjectByName(category + "Dropdown[" + i + "]");
 		control.onSelectionChange = function(){};  // just the time to setup the value
 		let config;
@@ -259,7 +263,7 @@
 			}
 		}
 
-		onUpdate = function(key)
+		control.onSelectionChange = function(key)
 		{
 			return function()
 			{
@@ -269,8 +273,8 @@
 			};
 		}(key);
 
-		control.onSelectionChange = onUpdate;
 		break;
+	}
 	default:
 		warn("Unknown option type " + option.type + ", assuming string.");
 		control = Engine.GetGUIObjectByName(category + "Input[" + i + "]");