polyfill assign for ie11

package.json

@@ -19,7 +19,7 @@
     "url": "https://github.com/Microsoft/monaco-editor/issues"
   },
   "devDependencies": {
-    "monaco-editor-core": "0.16.0",
+    "monaco-editor-core": "^0.16.1",
     "monaco-languages": "^1.7.0",
     "monaco-plugin-helpers": "^1.0.2",
     "requirejs": "^2.3.6",

src/fillers/polyfills.ts

@@ -0,0 +1,31 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+export function polyfill() {
+
+    // Object.assign, for IE11
+    if (typeof Object['assign'] != 'function') {
+        Object.defineProperty(Object, "assign", {
+            value: function assign(destination, sources) {
+                'use strict';
+                if (destination !== null) {
+                    for (let i = 1; i < arguments.length; i++) {
+                        const source = arguments[i];
+                        if (source) {
+                            for (var key in source) {
+                                if (Object.prototype.hasOwnProperty.call(source, key)) {
+                                    destination[key] = source[key]
+                                }
+                            }
+                        }
+                    };
+                }
+                return destination;
+            },
+            writable: true,
+            configurable: true
+        });
+    }
+}

src/htmlWorker.ts

@@ -11,6 +11,9 @@ import Thenable = monaco.Thenable;
 import * as htmlService from 'vscode-html-languageservice';
 import * as ls from 'vscode-languageserver-types';
 
+import * as poli from './fillers/polyfills';
+
+poli.polyfill();
 
 export class HTMLWorker {