Backport relevant parts of @webcomponents/platform

Author: TimvdLippe

.editorconfig

@@ -0,0 +1,8 @@
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = space
+indent_size = 2

packages/webcomponentsjs/src/platform/custom-event.js

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+/**
+ * @license
+ * Copyright (c) 2016 The Polymer Project Authors. All rights reserved.
+ * This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+ * The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+ * The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+ * Code distributed by Google as part of the polymer project is also
+ * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+ */
+
+(function() {
+  'use strict';
+
+  // defaultPrevented is broken in IE.
+  // https://connect.microsoft.com/IE/feedback/details/790389/event-defaultprevented-returns-false-after-preventdefault-was-called
+  var workingDefaultPrevented = (function() {
+    var e = document.createEvent('Event');
+    e.initEvent('foo', true, true);
+    e.preventDefault();
+    return e.defaultPrevented;
+  })();
+
+  if (!workingDefaultPrevented) {
+    var origPreventDefault = Event.prototype.preventDefault;
+    Event.prototype.preventDefault = function() {
+      if (!this.cancelable) {
+        return;
+      }
+
+      origPreventDefault.call(this);
+
+      Object.defineProperty(this, 'defaultPrevented', {
+        get: function() {
+          return true;
+        },
+        configurable: true
+      });
+    };
+  }
+
+  var isIE = /Trident/.test(navigator.userAgent);
+
+  // Event constructor shim
+  if (!window.Event || isIE && (typeof window.Event !== 'function')) {
+    var origEvent = window.Event;
+    /**
+     * @param {!string} inType
+     * @param {?(EventInit)=} params
+     */
+    window.Event = function(inType, params) {
+      params = params || {};
+      var e = document.createEvent('Event');
+      e.initEvent(inType, Boolean(params.bubbles), Boolean(params.cancelable));
+      return e;
+    };
+    if (origEvent) {
+      for (var i in origEvent) {
+        window.Event[i] = origEvent[i];
+      }
+      window.Event.prototype = origEvent.prototype;
+    }
+  }
+
+  // CustomEvent constructor shim
+  if (!window.CustomEvent || isIE && (typeof window.CustomEvent !== 'function')) {
+    /**
+     * @template T
+     * @param {!string} inType
+     * @param {?(CustomEventInit<T>)=} params
+     */
+    window.CustomEvent = function(inType, params) {
+      params = params || {};
+      var e = document.createEvent('CustomEvent');
+      e.initCustomEvent(inType, Boolean(params.bubbles), Boolean(params.cancelable), params.detail);
+      return e;
+    };
+    window.CustomEvent.prototype = window.Event.prototype;
+  }
+
+  if (!window.MouseEvent || isIE && (typeof window.MouseEvent !== 'function')) {
+    var origMouseEvent = window.MouseEvent;
+    /**
+     *
+     * @param {!string} inType
+     * @param {?(MouseEventInit)=} params
+     */
+    window.MouseEvent = function(inType, params) {
+      params = params || {};
+      var e = document.createEvent('MouseEvent');
+      e.initMouseEvent(inType,
+        Boolean(params.bubbles), Boolean(params.cancelable),
+        params.view || window, params.detail,
+        params.screenX, params.screenY, params.clientX, params.clientY,
+        params.ctrlKey, params.altKey, params.shiftKey, params.metaKey,
+        params.button, params.relatedTarget);
+      return e;
+    };
+    if (origMouseEvent) {
+      for (var i in origMouseEvent) {
+        window.MouseEvent[i] = origMouseEvent[i];
+      }
+    }
+    window.MouseEvent.prototype = origMouseEvent.prototype;
+  }
+})();

packages/webcomponentsjs/src/platform/es6-misc.js

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+/**
+ * @license
+ * Copyright (c) 2016 The Polymer Project Authors. All rights reserved.
+ * This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+ * The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+ * The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+ * Code distributed by Google as part of the polymer project is also
+ * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+ */
+
+(function() {
+  'use strict';
+
+  if (!Array.from) {
+    Array.from = function (object) {
+      return [].slice.call(/** @type {IArrayLike} */(object));
+    };
+  }
+
+  if (!Object.assign) {
+    var assign = function(target, source) {
+      var n$ = Object.getOwnPropertyNames(source);
+      for (var i=0, p; i < n$.length; i++) {
+        p = n$[i];
+        target[p] = source[p];
+      }
+    }
+
+    Object.assign = function(target, sources) {
+      var args = [].slice.call(arguments, 1);
+      for (var i=0, s; i < args.length; i++) {
+        s = args[i];
+        if (s) {
+          assign(target, s);
+        }
+      }
+      return target;
+    }
+  }
+})();