diff --git a/misc/dist/html/editor.html b/misc/dist/html/editor.html
index c2cfd96da5b..b4a8c69cc63 100644
--- a/misc/dist/html/editor.html
+++ b/misc/dist/html/editor.html
@@ -236,7 +236,7 @@
 	<script type='text/javascript' src='godot.tools.js'></script>
 	<script type='text/javascript'>//<![CDATA[
 
-		var engine = new Engine;
+		var editor = null;
 		var game = null;
 		var setStatusMode;
 		var setStatusNotice;
@@ -321,8 +321,8 @@
 
 		function closeEditor() {
 			closeGame();
-			if (engine) {
-				engine.requestQuit();
+			if (editor) {
+				editor.requestQuit();
 			}
 		}
 
@@ -336,6 +336,7 @@
 			var statusProgressInner = document.getElementById('status-progress-inner');
 			var statusIndeterminate = document.getElementById('status-indeterminate');
 			var statusNotice = document.getElementById('status-notice');
+			var headerDiv = document.getElementById('tabs-buttons');
 
 			var initializing = true;
 			var statusMode = 'hidden';
@@ -349,16 +350,23 @@
 			}
 			requestAnimationFrame(animate);
 
+			var lastScale = 0;
+			var lastWidth = 0;
+			var lastHeight = 0;
 			function adjustCanvasDimensions() {
 				var scale = window.devicePixelRatio || 1;
-				var header = document.getElementById('tabs-buttons');
-				var headerHeight = header.offsetHeight + 1;
+				var headerHeight = headerDiv.offsetHeight + 1;
 				var width = window.innerWidth;
 				var height = window.innerHeight - headerHeight;
-				editorCanvas.width = width * scale;
-				editorCanvas.height = height * scale;
-				editorCanvas.style.width = width + "px";
-				editorCanvas.style.height = height + "px";
+				if (lastScale !== scale || lastWidth !== width || lastHeight !== height) {
+					editorCanvas.width = width * scale;
+					editorCanvas.height = height * scale;
+					editorCanvas.style.width = width + "px";
+					editorCanvas.style.height = height + "px";
+					lastScale = scale;
+					lastWidth = width;
+					lastHeight = height;
+				}
 			}
 			animationCallbacks.push(adjustCanvasDimensions);
 			adjustCanvasDimensions();
@@ -412,24 +420,23 @@
 				});
 			};
 
-			engine.setProgressFunc((current, total) => {
-				if (total > 0) {
-					statusProgressInner.style.width = current/total * 100 + '%';
-					setStatusMode('progress');
-					if (current === total) {
-						// wait for progress bar animation
-						setTimeout(() => {
-							setStatusMode('indeterminate');
-						}, 100);
-					}
-				} else {
-					setStatusMode('indeterminate');
-				}
-			});
+			const gameConfig = {
+				'persistentPaths': persistentPaths,
+				'unloadAfterInit': false,
+				'canvas': gameCanvas,
+				'canvasResizePolicy': 1,
+				'onExit': function () {
+					setGameTabEnabled(false);
+					showTab('editor');
+					game = null;
+				},
+			};
 
-			engine.setPersistentPaths(persistentPaths);
-
-			engine.setOnExecute(function(args) {
+			var OnEditorExit = function () {
+				showTab('loader');
+				setLoaderEnabled(true);
+			};
+			function Execute(args) {
 				const is_editor = args.filter(function(v) { return v == '--editor' || v == '-e' }).length != 0;
 				const is_project_manager = args.filter(function(v) { return v == '--project-manager' }).length != 0;
 				const is_game = !is_editor && !is_project_manager;
@@ -442,42 +449,60 @@
 						return;
 					}
 					setGameTabEnabled(true);
-					game = new Engine();
-					game.setPersistentPaths(persistentPaths);
-					game.setUnloadAfterInit(false);
-					game.setOnExecute(engine.onExecute);
-					game.setCanvas(gameCanvas);
-					game.setCanvasResizedOnStart(true);
-					game.setOnExit(function() {
-						setGameTabEnabled(false);
-						showTab('editor');
-						game = null;
-					});
+					game = new Engine(gameConfig);
 					showTab('game');
 					game.init().then(function() {
 						requestAnimationFrame(function() {
-							game.start.apply(game, args).then(function() {
+							game.start({'args': args}).then(function() {
 								gameCanvas.focus();
 							});
 						});
 					});
 				} else { // New editor instances will be run in the same canvas. We want to wait for it to exit.
-					engine.setOnExit(function(code) {
+					OnEditorExit = function(code) {
 						setLoaderEnabled(true);
 						setTimeout(function() {
-							engine.init().then(function() {
+							editor.init().then(function() {
 								setLoaderEnabled(false);
-								engine.setOnExit(function() {
+								OnEditorExit = function() {
 									showTab('loader');
 									setLoaderEnabled(true);
-								});
-								engine.start.apply(engine, args);
+								};
+								editor.start({'args': args});
 							});
 						}, 0);
-						engine.setOnExit(null);
-					});
+						OnEditorExit = null;
+					};
 				}
-			});
+			}
+
+			const editorConfig = {
+				'unloadAfterInit': false,
+				'onProgress': function progressFunction (current, total) {
+					if (total > 0) {
+						statusProgressInner.style.width = current/total * 100 + '%';
+						setStatusMode('progress');
+						if (current === total) {
+							// wait for progress bar animation
+							setTimeout(() => {
+								setStatusMode('indeterminate');
+							}, 100);
+						}
+					} else {
+						setStatusMode('indeterminate');
+					}
+				},
+				'canvas': editorCanvas,
+				'canvasResizePolicy': 0,
+				'onExit': function() {
+					if (OnEditorExit) {
+						OnEditorExit();
+					}
+				},
+				'onExecute': Execute,
+				'persistentPaths': persistentPaths,
+			};
+			editor = new Engine(editorConfig);
 
 			function displayFailureNotice(err) {
 				var msg = err.message || err;
@@ -491,26 +516,20 @@
 				displayFailureNotice('WebGL not available');
 			} else {
 				setStatusMode('indeterminate');
-				engine.setCanvas(editorCanvas);
-				engine.setUnloadAfterInit(false); // Don't want to reload when starting game.
-				engine.init('godot.tools').then(function() {
+				editor.init('godot.tools').then(function() {
 					if (zip) {
-						engine.copyToFS("/tmp/preload.zip", zip);
+						editor.copyToFS("/tmp/preload.zip", zip);
 					}
 					try {
 						// Avoid user creating project in the persistent root folder.
-						engine.copyToFS("/home/web_user/keep", new Uint8Array());
+						editor.copyToFS("/home/web_user/keep", new Uint8Array());
 					} catch(e) {
 						// File exists
 					}
 					//selectVideoMode();
 					showTab('editor');
 					setLoaderEnabled(false);
-					engine.setOnExit(function() {
-						showTab('loader');
-						setLoaderEnabled(true);
-					});
-					engine.start('--video-driver', video_driver).then(function() {
+					editor.start({'args': ['--video-driver', video_driver]}).then(function() {
 						setStatusMode('hidden');
 						initializing = false;
 					});
diff --git a/misc/dist/html/full-size.html b/misc/dist/html/full-size.html
index 85c5305b85f..c7e657e53da 100644
--- a/misc/dist/html/full-size.html
+++ b/misc/dist/html/full-size.html
@@ -134,21 +134,14 @@ $GODOT_HEAD_INCLUDE
 		<div id='status-notice' class='godot' style='display: none;'></div>
 	</div>
 
-	<script type='text/javascript' src='$GODOT_BASENAME.js'></script>
+	<script type='text/javascript' src='$GODOT_URL'></script>
 	<script type='text/javascript'>//<![CDATA[
 
-		var engine = new Engine;
-		var setStatusMode;
-		var setStatusNotice;
+		const GODOT_CONFIG = $GODOT_CONFIG;
+		var engine = new Engine(GODOT_CONFIG);
 
 		(function() {
-			const EXECUTABLE_NAME = '$GODOT_BASENAME';
-			const MAIN_PACK = '$GODOT_BASENAME.pck';
-			const EXTRA_ARGS = JSON.parse('$GODOT_ARGS');
-			const GDNATIVE_LIBS = [$GODOT_GDNATIVE_LIBS];
 			const INDETERMINATE_STATUS_STEP_MS = 100;
-			const FULL_WINDOW = $GODOT_FULL_WINDOW;
-
 			var canvas = document.getElementById('canvas');
 			var statusProgress = document.getElementById('status-progress');
 			var statusProgressInner = document.getElementById('status-progress-inner');
@@ -180,14 +173,13 @@ $GODOT_HEAD_INCLUDE
 					canvas.style.height = lastHeight + "px";
 				}
 			}
-			if (FULL_WINDOW) {
+			if (GODOT_CONFIG['canvasResizePolicy'] == 2) {
 				animationCallbacks.push(adjustCanvasDimensions);
 				adjustCanvasDimensions();
-			} else {
-				engine.setCanvasResizedOnStart(true);
 			}
 
-			setStatusMode = function setStatusMode(mode) {
+			function setStatusMode(mode) {
+
 				if (statusMode === mode || !initializing)
 					return;
 				[statusProgress, statusIndeterminate, statusNotice].forEach(elem => {
@@ -213,7 +205,7 @@ $GODOT_HEAD_INCLUDE
 						throw new Error('Invalid status mode');
 				}
 				statusMode = mode;
-			};
+			}
 
 			function animateStatusIndeterminate(ms) {
 				var i = Math.floor(ms / INDETERMINATE_STATUS_STEP_MS % 8);
@@ -225,7 +217,7 @@ $GODOT_HEAD_INCLUDE
 				}
 			}
 
-			setStatusNotice = function setStatusNotice(text) {
+			function setStatusNotice(text) {
 				while (statusNotice.lastChild) {
 					statusNotice.removeChild(statusNotice.lastChild);
 				}
@@ -236,21 +228,6 @@ $GODOT_HEAD_INCLUDE
 				});
 			};
 
-			engine.setProgressFunc((current, total) => {
-				if (total > 0) {
-					statusProgressInner.style.width = current/total * 100 + '%';
-					setStatusMode('progress');
-					if (current === total) {
-						// wait for progress bar animation
-						setTimeout(() => {
-							setStatusMode('indeterminate');
-						}, 500);
-					}
-				} else {
-					setStatusMode('indeterminate');
-				}
-			});
-
 			function displayFailureNotice(err) {
 				var msg = err.message || err;
 				console.error(msg);
@@ -263,9 +240,22 @@ $GODOT_HEAD_INCLUDE
 				displayFailureNotice('WebGL not available');
 			} else {
 				setStatusMode('indeterminate');
-				engine.setCanvas(canvas);
-				engine.setGDNativeLibraries(GDNATIVE_LIBS);
-				engine.startGame(EXECUTABLE_NAME, MAIN_PACK, EXTRA_ARGS).then(() => {
+				engine.startGame({
+					'onProgress': function (current, total) {
+						if (total > 0) {
+							statusProgressInner.style.width = current/total * 100 + '%';
+							setStatusMode('progress');
+							if (current === total) {
+								// wait for progress bar animation
+								setTimeout(() => {
+									setStatusMode('indeterminate');
+								}, 500);
+							}
+						} else {
+							setStatusMode('indeterminate');
+						}
+					},
+				}).then(() => {
 					setStatusMode('hidden');
 					initializing = false;
 				}, displayFailureNotice);
diff --git a/platform/javascript/.eslintrc.engine.js b/platform/javascript/.eslintrc.engine.js
index 00f0f147a94..3725cf164ed 100644
--- a/platform/javascript/.eslintrc.engine.js
+++ b/platform/javascript/.eslintrc.engine.js
@@ -3,6 +3,7 @@ module.exports = {
 		"./.eslintrc.js",
 	],
 	"globals": {
+		"EngineConfig": true,
 		"Godot": true,
 		"Preloader": true,
 		"Utils": true,
diff --git a/platform/javascript/SCsub b/platform/javascript/SCsub
index 11a45d28117..ab527ef4191 100644
--- a/platform/javascript/SCsub
+++ b/platform/javascript/SCsub
@@ -74,6 +74,7 @@ sys_env.Depends(build[0], sys_env["JS_EXTERNS"])
 engine = [
     "js/engine/preloader.js",
     "js/engine/utils.js",
+    "js/engine/config.js",
     "js/engine/engine.js",
 ]
 externs = [env.File("#platform/javascript/js/engine/engine.externs.js")]
diff --git a/platform/javascript/display_server_javascript.cpp b/platform/javascript/display_server_javascript.cpp
index 5e2dddd8e73..92f3152ba72 100644
--- a/platform/javascript/display_server_javascript.cpp
+++ b/platform/javascript/display_server_javascript.cpp
@@ -749,7 +749,7 @@ DisplayServerJavaScript::DisplayServerJavaScript(const String &p_rendering_drive
 #endif
 
 	window_set_mode(p_mode);
-	if (godot_js_config_is_resize_on_start()) {
+	if (godot_js_config_canvas_resize_policy_get() == 1) {
 		window_set_size(p_resolution);
 	}
 
diff --git a/platform/javascript/export/export.cpp b/platform/javascript/export/export.cpp
index 199d778314d..fa8b000259f 100644
--- a/platform/javascript/export/export.cpp
+++ b/platform/javascript/export/export.cpp
@@ -285,24 +285,29 @@ void EditorExportPlatformJavaScript::_fix_html(Vector<uint8_t> &p_html, const Re
 	String str_template = String::utf8(reinterpret_cast<const char *>(p_html.ptr()), p_html.size());
 	String str_export;
 	Vector<String> lines = str_template.split("\n");
-	Vector<String> flags;
-	String flags_json;
-	gen_export_flags(flags, p_flags);
-	flags_json = JSON::print(flags);
-	String libs;
+	Array libs;
 	for (int i = 0; i < p_shared_objects.size(); i++) {
-		libs += "\"" + p_shared_objects[i].path.get_file() + "\",";
+		libs.push_back(p_shared_objects[i].path.get_file());
 	}
+	Vector<String> flags;
+	gen_export_flags(flags, p_flags & (~DEBUG_FLAG_DUMB_CLIENT));
+	Array args;
+	for (int i = 0; i < flags.size(); i++) {
+		args.push_back(flags[i]);
+	}
+	Dictionary config;
+	config["canvasResizePolicy"] = p_preset->get("html/full_window_size") ? 2 : 1;
+	config["gdnativeLibs"] = libs;
+	config["executable"] = p_name;
+	config["args"] = args;
+	const String str_config = JSON::print(config);
 
 	for (int i = 0; i < lines.size(); i++) {
 		String current_line = lines[i];
-		current_line = current_line.replace("$GODOT_BASENAME", p_name);
+		current_line = current_line.replace("$GODOT_URL", p_name + ".js");
 		current_line = current_line.replace("$GODOT_PROJECT_NAME", ProjectSettings::get_singleton()->get_setting("application/config/name"));
 		current_line = current_line.replace("$GODOT_HEAD_INCLUDE", p_preset->get("html/head_include"));
-		current_line = current_line.replace("$GODOT_FULL_WINDOW", p_preset->get("html/full_window_size") ? "true" : "false");
-		current_line = current_line.replace("$GODOT_GDNATIVE_LIBS", libs);
-		current_line = current_line.replace("$GODOT_DEBUG_ENABLED", p_debug ? "true" : "false");
-		current_line = current_line.replace("$GODOT_ARGS", flags_json);
+		current_line = current_line.replace("$GODOT_CONFIG", str_config);
 		str_export += current_line + "\n";
 	}
 
diff --git a/platform/javascript/godot_js.h b/platform/javascript/godot_js.h
index f0da8b7ca39..81443de7a2b 100644
--- a/platform/javascript/godot_js.h
+++ b/platform/javascript/godot_js.h
@@ -40,7 +40,7 @@ extern "C" {
 // Config
 extern void godot_js_config_locale_get(char *p_ptr, int p_ptr_max);
 extern void godot_js_config_canvas_id_get(char *p_ptr, int p_ptr_max);
-extern int godot_js_config_is_resize_on_start();
+extern int godot_js_config_canvas_resize_policy_get();
 
 // OS
 extern void godot_js_os_finish_async(void (*p_callback)());
diff --git a/platform/javascript/js/engine/config.js b/platform/javascript/js/engine/config.js
new file mode 100644
index 00000000000..97fd7188151
--- /dev/null
+++ b/platform/javascript/js/engine/config.js
@@ -0,0 +1,100 @@
+/** @constructor */
+function EngineConfig(opts) {
+	// Module config
+	this.unloadAfterInit = true;
+	this.onPrintError = function () {
+		console.error.apply(console, Array.from(arguments)); // eslint-disable-line no-console
+	};
+	this.onPrint = function () {
+		console.log.apply(console, Array.from(arguments)); // eslint-disable-line no-console
+	};
+	this.onProgress = null;
+
+	// Godot Config
+	this.canvas = null;
+	this.executable = '';
+	this.mainPack = null;
+	this.locale = null;
+	this.canvasResizePolicy = false;
+	this.persistentPaths = ['/userfs'];
+	this.gdnativeLibs = [];
+	this.args = [];
+	this.onExecute = null;
+	this.onExit = null;
+	this.update(opts);
+}
+
+EngineConfig.prototype.update = function (opts) {
+	const config = opts || {};
+	function parse(key, def) {
+		if (typeof (config[key]) === 'undefined') {
+			return def;
+		}
+		return config[key];
+	}
+	// Module config
+	this.unloadAfterInit = parse('unloadAfterInit', this.unloadAfterInit);
+	this.onPrintError = parse('onPrintError', this.onPrintError);
+	this.onPrint = parse('onPrint', this.onPrint);
+	this.onProgress = parse('onProgress', this.onProgress);
+
+	// Godot config
+	this.canvas = parse('canvas', this.canvas);
+	this.executable = parse('executable', this.executable);
+	this.mainPack = parse('mainPack', this.mainPack);
+	this.locale = parse('locale', this.locale);
+	this.canvasResizePolicy = parse('canvasResizePolicy', this.canvasResizePolicy);
+	this.persistentPaths = parse('persistentPaths', this.persistentPaths);
+	this.gdnativeLibs = parse('gdnativeLibs', this.gdnativeLibs);
+	this.args = parse('args', this.args);
+	this.onExecute = parse('onExecute', this.onExecute);
+	this.onExit = parse('onExit', this.onExit);
+};
+
+EngineConfig.prototype.getModuleConfig = function (loadPath, loadPromise) {
+	const me = this;
+	return {
+		'print': this.onPrint,
+		'printErr': this.onPrintError,
+		'locateFile': Utils.createLocateRewrite(loadPath),
+		'instantiateWasm': Utils.createInstantiatePromise(loadPromise),
+		'thisProgram': me.executable,
+		'noExitRuntime': true,
+		'dynamicLibraries': [`${me.executable}.side.wasm`],
+	};
+};
+
+EngineConfig.prototype.getGodotConfig = function (cleanup) {
+	if (!(this.canvas instanceof HTMLCanvasElement)) {
+		this.canvas = Utils.findCanvas();
+		if (!this.canvas) {
+			throw new Error('No canvas found in page');
+		}
+	}
+
+	// Canvas can grab focus on click, or key events won't work.
+	if (this.canvas.tabIndex < 0) {
+		this.canvas.tabIndex = 0;
+	}
+
+	// Browser locale, or custom one if defined.
+	let locale = this.locale;
+	if (!locale) {
+		locale = navigator.languages ? navigator.languages[0] : navigator.language;
+		locale = locale.split('.')[0];
+	}
+	const onExit = this.onExit;
+	// Godot configuration.
+	return {
+		'canvas': this.canvas,
+		'canvasResizePolicy': this.canvasResizePolicy,
+		'locale': locale,
+		'onExecute': this.onExecute,
+		'onExit': function (p_code) {
+			cleanup(); // We always need to call the cleanup callback to free memory.
+			if (typeof (onExit) === 'function') {
+				onExit(p_code);
+			}
+		},
+	};
+};
diff --git a/platform/javascript/js/engine/engine.js b/platform/javascript/js/engine/engine.js
index 321221323cc..d14e0e58064 100644
--- a/platform/javascript/js/engine/engine.js
+++ b/platform/javascript/js/engine/engine.js
@@ -1,20 +1,14 @@
 const Engine = (function () {
 	const preloader = new Preloader();
 
-	let wasmExt = '.wasm';
-	let unloadAfterInit = true;
-	let loadPath = '';
 	let loadPromise = null;
+	let loadPath = '';
 	let initPromise = null;
-	let stderr = null;
-	let stdout = null;
-	let progressFunc = null;
 
 	function load(basePath) {
 		if (loadPromise == null) {
 			loadPath = basePath;
-			loadPromise = preloader.loadPromise(basePath + wasmExt);
-			preloader.setProgressFunc(progressFunc);
+			loadPromise = preloader.loadPromise(`${loadPath}.wasm`);
 			requestAnimationFrame(preloader.animateProgress);
 		}
 		return loadPromise;
@@ -25,16 +19,9 @@ const Engine = (function () {
 	}
 
 	/** @constructor */
-	function Engine() { // eslint-disable-line no-shadow
-		this.canvas = null;
-		this.executableName = '';
+	function Engine(opts) { // eslint-disable-line no-shadow
+		this.config = new EngineConfig(opts);
 		this.rtenv = null;
-		this.customLocale = null;
-		this.resizeCanvasOnStart = false;
-		this.onExecute = null;
-		this.onExit = null;
-		this.persistentPaths = ['/userfs'];
-		this.gdnativeLibs = [];
 	}
 
 	Engine.prototype.init = /** @param {string=} basePath */ function (basePath) {
@@ -48,25 +35,14 @@ const Engine = (function () {
 			}
 			load(basePath);
 		}
-		let config = {};
-		if (typeof stdout === 'function') {
-			config.print = stdout;
-		}
-		if (typeof stderr === 'function') {
-			config.printErr = stderr;
-		}
+		preloader.setProgressFunc(this.config.onProgress);
+		let config = this.config.getModuleConfig(loadPath, loadPromise);
 		const me = this;
 		initPromise = new Promise(function (resolve, reject) {
-			config['locateFile'] = Utils.createLocateRewrite(loadPath);
-			config['instantiateWasm'] = Utils.createInstantiatePromise(loadPromise);
-			// Emscripten configuration.
-			config['thisProgram'] = me.executableName;
-			config['noExitRuntime'] = true;
-			config['dynamicLibraries'] = [`${me.executableName}.side.wasm`].concat(me.gdnativeLibs);
 			Godot(config).then(function (module) {
-				module['initFS'](me.persistentPaths).then(function (fs_err) {
+				module['initFS'](me.config.persistentPaths).then(function (fs_err) {
 					me.rtenv = module;
-					if (unloadAfterInit) {
+					if (me.config.unloadAfterInit) {
 						unload();
 					}
 					resolve();
@@ -83,152 +59,60 @@ const Engine = (function () {
 	};
 
 	/** @type {function(...string):Object} */
-	Engine.prototype.start = function () {
-		// Start from arguments.
-		const args = [];
-		for (let i = 0; i < arguments.length; i++) {
-			args.push(arguments[i]);
-		}
+	Engine.prototype.start = function (override) {
+		this.config.update(override);
 		const me = this;
 		return me.init().then(function () {
 			if (!me.rtenv) {
 				return Promise.reject(new Error('The engine must be initialized before it can be started'));
 			}
 
-			if (!(me.canvas instanceof HTMLCanvasElement)) {
-				me.canvas = Utils.findCanvas();
-				if (!me.canvas) {
-					return Promise.reject(new Error('No canvas found in page'));
-				}
-			}
-
-			// Canvas can grab focus on click, or key events won't work.
-			if (me.canvas.tabIndex < 0) {
-				me.canvas.tabIndex = 0;
-			}
-
-			// Browser locale, or custom one if defined.
-			let locale = me.customLocale;
-			if (!locale) {
-				locale = navigator.languages ? navigator.languages[0] : navigator.language;
-				locale = locale.split('.')[0];
+			let config = {};
+			try {
+				config = me.config.getGodotConfig(function () {
+					me.rtenv = null;
+				});
+			} catch (e) {
+				return Promise.reject(e);
 			}
 			// Godot configuration.
-			me.rtenv['initConfig']({
-				'resizeCanvasOnStart': me.resizeCanvasOnStart,
-				'canvas': me.canvas,
-				'locale': locale,
-				'onExecute': function (p_args) {
-					if (me.onExecute) {
-						me.onExecute(p_args);
-						return 0;
-					}
-					return 1;
-				},
-				'onExit': function (p_code) {
-					me.rtenv['deinitFS']();
-					if (me.onExit) {
-						me.onExit(p_code);
-					}
-					me.rtenv = null;
-				},
-			});
+			me.rtenv['initConfig'](config);
 
-			return new Promise(function (resolve, reject) {
-				preloader.preloadedFiles.forEach(function (file) {
-					me.rtenv['copyToFS'](file.path, file.buffer);
+			// Preload GDNative libraries.
+			const libs = [];
+			me.config.gdnativeLibs.forEach(function (lib) {
+				libs.push(me.rtenv['loadDynamicLibrary'](lib, { 'loadAsync': true }));
+			});
+			return Promise.all(libs).then(function () {
+				return new Promise(function (resolve, reject) {
+					preloader.preloadedFiles.forEach(function (file) {
+						me.rtenv['copyToFS'](file.path, file.buffer);
+					});
+					preloader.preloadedFiles.length = 0; // Clear memory
+					me.rtenv['callMain'](me.config.args);
+					initPromise = null;
+					resolve();
 				});
-				preloader.preloadedFiles.length = 0; // Clear memory
-				me.rtenv['callMain'](args);
-				initPromise = null;
-				resolve();
 			});
 		});
 	};
 
-	Engine.prototype.startGame = function (execName, mainPack, extraArgs) {
+	Engine.prototype.startGame = function (override) {
+		this.config.update(override);
+		// Add main-pack argument.
+		const exe = this.config.executable;
+		const pack = this.config.mainPack || `${exe}.pck`;
+		this.config.args = ['--main-pack', pack].concat(this.config.args);
 		// Start and init with execName as loadPath if not inited.
-		this.executableName = execName;
 		const me = this;
 		return Promise.all([
-			this.init(execName),
-			this.preloadFile(mainPack, mainPack),
+			this.init(exe),
+			this.preloadFile(pack, pack),
 		]).then(function () {
-			let args = ['--main-pack', mainPack];
-			if (extraArgs) {
-				args = args.concat(extraArgs);
-			}
-			return me.start.apply(me, args);
+			return me.start.apply(me);
 		});
 	};
 
-	Engine.prototype.setWebAssemblyFilenameExtension = function (override) {
-		if (String(override).length === 0) {
-			throw new Error('Invalid WebAssembly filename extension override');
-		}
-		wasmExt = String(override);
-	};
-
-	Engine.prototype.setUnloadAfterInit = function (enabled) {
-		unloadAfterInit = enabled;
-	};
-
-	Engine.prototype.setCanvas = function (canvasElem) {
-		this.canvas = canvasElem;
-	};
-
-	Engine.prototype.setCanvasResizedOnStart = function (enabled) {
-		this.resizeCanvasOnStart = enabled;
-	};
-
-	Engine.prototype.setLocale = function (locale) {
-		this.customLocale = locale;
-	};
-
-	Engine.prototype.setExecutableName = function (newName) {
-		this.executableName = newName;
-	};
-
-	Engine.prototype.setProgressFunc = function (func) {
-		progressFunc = func;
-	};
-
-	Engine.prototype.setStdoutFunc = function (func) {
-		const print = function (text) {
-			let msg = text;
-			if (arguments.length > 1) {
-				msg = Array.prototype.slice.call(arguments).join(' ');
-			}
-			func(msg);
-		};
-		if (this.rtenv) {
-			this.rtenv.print = print;
-		}
-		stdout = print;
-	};
-
-	Engine.prototype.setStderrFunc = function (func) {
-		const printErr = function (text) {
-			let msg = text;
-			if (arguments.length > 1) {
-				msg = Array.prototype.slice.call(arguments).join(' ');
-			}
-			func(msg);
-		};
-		if (this.rtenv) {
-			this.rtenv.printErr = printErr;
-		}
-		stderr = printErr;
-	};
-
-	Engine.prototype.setOnExecute = function (onExecute) {
-		this.onExecute = onExecute;
-	};
-
-	Engine.prototype.setOnExit = function (onExit) {
-		this.onExit = onExit;
-	};
-
 	Engine.prototype.copyToFS = function (path, buffer) {
 		if (this.rtenv == null) {
 			throw new Error('Engine must be inited before copying files');
@@ -236,14 +120,6 @@ const Engine = (function () {
 		this.rtenv['copyToFS'](path, buffer);
 	};
 
-	Engine.prototype.setPersistentPaths = function (persistentPaths) {
-		this.persistentPaths = persistentPaths;
-	};
-
-	Engine.prototype.setGDNativeLibraries = function (gdnativeLibs) {
-		this.gdnativeLibs = gdnativeLibs;
-	};
-
 	Engine.prototype.requestQuit = function () {
 		if (this.rtenv) {
 			this.rtenv['request_quit']();
@@ -259,20 +135,7 @@ const Engine = (function () {
 	Engine.prototype['preloadFile'] = Engine.prototype.preloadFile;
 	Engine.prototype['start'] = Engine.prototype.start;
 	Engine.prototype['startGame'] = Engine.prototype.startGame;
-	Engine.prototype['setWebAssemblyFilenameExtension'] = Engine.prototype.setWebAssemblyFilenameExtension;
-	Engine.prototype['setUnloadAfterInit'] = Engine.prototype.setUnloadAfterInit;
-	Engine.prototype['setCanvas'] = Engine.prototype.setCanvas;
-	Engine.prototype['setCanvasResizedOnStart'] = Engine.prototype.setCanvasResizedOnStart;
-	Engine.prototype['setLocale'] = Engine.prototype.setLocale;
-	Engine.prototype['setExecutableName'] = Engine.prototype.setExecutableName;
-	Engine.prototype['setProgressFunc'] = Engine.prototype.setProgressFunc;
-	Engine.prototype['setStdoutFunc'] = Engine.prototype.setStdoutFunc;
-	Engine.prototype['setStderrFunc'] = Engine.prototype.setStderrFunc;
-	Engine.prototype['setOnExecute'] = Engine.prototype.setOnExecute;
-	Engine.prototype['setOnExit'] = Engine.prototype.setOnExit;
 	Engine.prototype['copyToFS'] = Engine.prototype.copyToFS;
-	Engine.prototype['setPersistentPaths'] = Engine.prototype.setPersistentPaths;
-	Engine.prototype['setGDNativeLibraries'] = Engine.prototype.setGDNativeLibraries;
 	Engine.prototype['requestQuit'] = Engine.prototype.requestQuit;
 	return Engine;
 }());
diff --git a/platform/javascript/js/libs/library_godot_os.js b/platform/javascript/js/libs/library_godot_os.js
index 3ffcd655b7e..ef6df17e97c 100644
--- a/platform/javascript/js/libs/library_godot_os.js
+++ b/platform/javascript/js/libs/library_godot_os.js
@@ -58,21 +58,28 @@ const GodotConfig = {
 	$GodotConfig: {
 		canvas: null,
 		locale: 'en',
-		resize_on_start: false,
+		canvas_resize_policy: 2, // Adaptive
 		on_execute: null,
+		on_exit: null,
 
 		init_config: function (p_opts) {
-			GodotConfig.resize_on_start = !!p_opts['resizeCanvasOnStart'];
+			GodotConfig.canvas_resize_policy = p_opts['canvasResizePolicy'];
 			GodotConfig.canvas = p_opts['canvas'];
 			GodotConfig.locale = p_opts['locale'] || GodotConfig.locale;
 			GodotConfig.on_execute = p_opts['onExecute'];
-			// This is called by emscripten, even if undocumented.
-			Module['onExit'] = p_opts['onExit']; // eslint-disable-line no-undef
+			GodotConfig.on_exit = p_opts['onExit'];
 		},
 
 		locate_file: function (file) {
 			return Module['locateFile'](file); // eslint-disable-line no-undef
 		},
+		clear: function () {
+			GodotConfig.canvas = null;
+			GodotConfig.locale = 'en';
+			GodotConfig.canvas_resize_policy = 2;
+			GodotConfig.on_execute = null;
+			GodotConfig.on_exit = null;
+		},
 	},
 
 	godot_js_config_canvas_id_get__sig: 'vii',
@@ -85,9 +92,9 @@ const GodotConfig = {
 		GodotRuntime.stringToHeap(GodotConfig.locale, p_ptr, p_ptr_max);
 	},
 
-	godot_js_config_is_resize_on_start__sig: 'i',
-	godot_js_config_is_resize_on_start: function () {
-		return GodotConfig.resize_on_start ? 1 : 0;
+	godot_js_config_canvas_resize_policy_get__sig: 'i',
+	godot_js_config_canvas_resize_policy_get: function () {
+		return GodotConfig.canvas_resize_policy;
 	},
 };
 
@@ -98,7 +105,6 @@ const GodotFS = {
 	$GodotFS__deps: ['$FS', '$IDBFS', '$GodotRuntime'],
 	$GodotFS__postset: [
 		'Module["initFS"] = GodotFS.init;',
-		'Module["deinitFS"] = GodotFS.deinit;',
 		'Module["copyToFS"] = GodotFS.copy_to_fs;',
 	].join(''),
 	$GodotFS: {
@@ -210,9 +216,10 @@ const GodotFS = {
 mergeInto(LibraryManager.library, GodotFS);
 
 const GodotOS = {
-	$GodotOS__deps: ['$GodotFS', '$GodotRuntime'],
+	$GodotOS__deps: ['$GodotRuntime', '$GodotConfig', '$GodotFS'],
 	$GodotOS__postset: [
 		'Module["request_quit"] = function() { GodotOS.request_quit() };',
+		'Module["onExit"] = GodotOS.cleanup;',
 		'GodotOS._fs_sync_promise = Promise.resolve();',
 	].join(''),
 	$GodotOS: {
@@ -224,6 +231,15 @@ const GodotOS = {
 			GodotOS._async_cbs.push(p_promise_cb);
 		},
 
+		cleanup: function (exit_code) {
+			const cb = GodotConfig.on_exit;
+			GodotFS.deinit();
+			GodotConfig.clear();
+			if (cb) {
+				cb(exit_code);
+			}
+		},
+
 		finish_async: function (callback) {
 			GodotOS._fs_sync_promise.then(function (err) {
 				const promises = [];