com.google.javascript.jscomp.js.es6.weakmap.js Maven / Gradle / Ivy

Show more of this group Show more artifacts with this name
Show all versions of closure-compiler-linter Show documentation

Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs. This binary checks for style issues such as incorrect or missing JSDoc usage, and missing goog.require() statements. It does not do more advanced checks such as typechecking.

There is a newer version: v20200830

Show newest version

/*
 * Copyright 2016 The Closure Compiler Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

'require es6/symbol';
'require es6/util/makeiterator';
'require util/defineproperty';
'require util/owns';
'require util/polyfill';

$jscomp.polyfill('WeakMap',
    /**
     * @param {*} NativeWeakMap
     * @return {*}
     * @suppress {reportUnknownTypes}
     */
    function(NativeWeakMap) {
  /**
   * Checks conformance of the existing WeakMap.
   * @return {boolean} True if the browser's implementation conforms.
   */
  function isConformant() {
    if (!NativeWeakMap || !Object.seal) return false;
    try {
      var x = Object.seal({});
      var y = Object.seal({});
      var map = new /** @type {function(new: WeakMap, !Array)} */ (
          NativeWeakMap)([[x, 2], [y, 3]]);
      if (map.get(x) != 2 || map.get(y) != 3) return false;
      map.delete(x);
      map.set(y, 4);
      return !map.has(x) && map.get(y) == 4;
    } catch (err) { // This should hopefully never happen, but let's be safe.
      return false;
    }
  }
  if (isConformant()) return NativeWeakMap;

  var prop = '$jscomp_hidden_' + Math.random().toString().substring(2);

  /**
   * Inserts the hidden property into the target.
   * @param {!Object} target
   */
  function insert(target) {
    if (!$jscomp.owns(target, prop)) {
      var obj = {};
      // TODO(sdh): This property will be enumerated in IE8.  If this becomes
      // a problem, we could avoid it by copying an infrequently-used non-enum
      // method (like toLocaleString) onto the object itself and encoding the
      // property on the copy instead.  This codepath must be easily removable
      // if IE8 support is not needed.
      $jscomp.defineProperty(target, prop, {value: obj});
    }
  }

  /**
   * Monkey-patches the freezing methods to ensure that the hidden
   * property is added before any freezing happens.
   * @param {string} name
   */
  function patch(name) {
    var prev = Object[name];
    if (prev) {
      Object[name] = function(target) {
        insert(target);
        return prev(target);
      };
    }
  }
  patch('freeze');
  patch('preventExtensions');
  patch('seal');
  // Note: no need to patch Reflect.preventExtensions since the polyfill
  // just calls Object.preventExtensions anyway (and if it's not polyfilled
  // then neither is WeakMap).

  var index = 0;

  /**
   * Polyfill for WeakMap:
   * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap
   *
   * This implementation is as non-leaky as possible, due to patching
   * the freezing and sealing operations.  It does not include any logic
   * to handle cases where a key was somehow made non-extensible without
   * the special hidden property being added.  It takes some care to ensure
   * the hidden property is not enumerated over nor discoverable, though
   * it's not completely secure (particularly in IE8).
   *
   * @constructor
   * @extends {WeakMap}
   * @template KEY, VALUE
   * @param {!Iterator>|!Array>|null=}
   *     opt_iterable Optional initial data.
   */
  var PolyfillWeakMap = function(opt_iterable) {
    /** @private @const {string} */
    this.id_ = (index += (Math.random() + 1)).toString();

    if (opt_iterable) {
      $jscomp.initSymbol();
      $jscomp.initSymbolIterator();
      var iter = $jscomp.makeIterator(opt_iterable);
      var entry;
      while (!(entry = iter.next()).done) {
        var item = entry.value;
        this.set(/** @type {KEY} */ (item[0]), /** @type {VALUE} */ (item[1]));
      }
    }
  };

  /** @override */
  PolyfillWeakMap.prototype.set = function(key, value) {
    insert(key);
    if (!$jscomp.owns(key, prop)) {
      // NOTE: If the insert() call fails on the key, but the property
      // has previously successfully been added higher up the prototype
      // chain, then we'll silently misbehave.  Instead, throw immediately
      // before doing something bad.  If this becomes a problem (e.g. due
      // to some rogue frozen objects) then we may need to add a slow and
      // leaky fallback array to each WeakMap instance, as well as extra
      // logic in each accessor to use it (*only*) when necessary.
      throw new Error('WeakMap key fail: ' + key);
    }
    key[prop][this.id_] = value;
    return this;
  };

  /** @override */
  PolyfillWeakMap.prototype.get = function(key) {
    return $jscomp.owns(key, prop) ? key[prop][this.id_] : undefined;
  };

  /** @override */
  PolyfillWeakMap.prototype.has = function(key) {
    return $jscomp.owns(key, prop) && $jscomp.owns(key[prop], this.id_);
  };

  /** @override */
  PolyfillWeakMap.prototype.delete = function(key) {
    if (!$jscomp.owns(key, prop) ||
        !$jscomp.owns(key[prop], this.id_)) {
      return false;
    }
    return delete key[prop][this.id_];
  };

  return PolyfillWeakMap;
}, 'es6-impl', 'es3');