weakmap.js

/*
 * Copyright 2012 The Polymer Authors. All rights reserved.
 * Use of this source code is governed by a BSD-style
 * license that can be found in the LICENSE file.
 */

if (typeof WeakMap === 'undefined') {
  (function() {
    var defineProperty = Object.defineProperty;
    var counter = Date.now() % 1e9;

    var WeakMap = function() {
      this.name = '__st' + (Math.random() * 1e9 >>> 0) + (counter++ + '__');
    };

    WeakMap.prototype = {
      set: function(key, value) {
        var entry = key[this.name];
        if (entry && entry[0] === key)
          entry[1] = value;
        else
          defineProperty(key, this.name, {value: [key, value], writable: true});
        return this;
      },
      get: function(key) {
        var entry;
        return (entry = key[this.name]) && entry[0] === key ?
            entry[1] : undefined;
      },
      delete: function(key) {
        var entry = key[this.name];
        if (!entry) return false;
        var hasValue = entry[0] === key;
        entry[0] = entry[1] = undefined;
        return hasValue;
      },
      has: function(key) {
        var entry = key[this.name];
        if (!entry) return false;
        return entry[0] === key;
      }
    };

    window.WeakMap = WeakMap;
  })();
}