Add Engine.setWebAssemblyFilenameExtension()

Some web game hosts only allow certain filename extensions. If .wasm is
not allowed, this function allows overriding the WebAssembly filename
extension to work around that restriction.

platform/javascript/engine.js

@@ -10,6 +10,7 @@
 	var DOWNLOAD_ATTEMPTS_MAX = 4;
 
 	var basePath = null;
+	var wasmFilenameExtensionOverride = null;
 	var engineLoadPromise = null;
 
 	var loadingFiles = {};
@@ -299,6 +300,14 @@
 		return !!testContext;
 	};
 
+	Engine.setWebAssemblyFilenameExtension = function(override) {
+
+		if (String(override).length === 0) {
+			throw new Error('Invalid WebAssembly filename extension override');
+		}
+		wasmFilenameExtensionOverride = String(override);
+	}
+
 	Engine.load = function(newBasePath) {
 
 		if (newBasePath !== undefined) basePath = getBasePath(newBasePath);
@@ -306,7 +315,7 @@
 			if (typeof WebAssembly !== 'object')
 				return Promise.reject(new Error("Browser doesn't support WebAssembly"));
 			// TODO cache/retrieve module to/from idb
-			engineLoadPromise = loadPromise(basePath + '.wasm').then(function(xhr) {
+			engineLoadPromise = loadPromise(basePath + '.' + (wasmFilenameExtensionOverride || 'wasm')).then(function(xhr) {
 				return xhr.response;
 			});
 			engineLoadPromise = engineLoadPromise.catch(function(err) {