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

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

There is a newer version: v20240317

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.
 */

/**
 * @fileoverview Symbol polyfill.
 * @suppress {uselessCode}
 */

'require es6/util/arrayiterator';
'require util/defineproperty';
'require util/global';
'require util/polyfill';

/**
 * Initializes the Symbol function.
 * @noinline
 */
// TODO(rishipal): Remove this function
$jscomp.initSymbol = function() {};

$jscomp.polyfill('Symbol', function(orig) {
  if (orig) return orig;  // no polyfill needed

  /**
   * @struct @constructor
   * @param {string} id
   * @param {string=} opt_description
   */
  var SymbolClass = function(id, opt_description) {
    /** @private @const {string} */
    this.$jscomp$symbol$id_ = id;

    /** @const {string|undefined} */
    this.description;

    // description is read-only.
    $jscomp.defineProperty(
        this, 'description',
        {configurable: true, writable: true, value: opt_description});
  };


  /** @override */
  SymbolClass.prototype.toString = function() {
    return this.$jscomp$symbol$id_;
  };


  /** @const {string} */
  var SYMBOL_PREFIX = 'jscomp_symbol_';

  var counter = 0;

  /**
   * Produces "symbols" (actually just unique strings).
   * @param {string=} opt_description
   * @return {!SymbolClass}
   * @this {?Object}
   */
  var symbolPolyfill = function(opt_description) {
    if (this instanceof symbolPolyfill) {
      throw new TypeError('Symbol is not a constructor');
    }
    return (new SymbolClass(
        SYMBOL_PREFIX + (opt_description || '') + '_' + (counter++),
        opt_description));
  };

  return symbolPolyfill;
}, 'es6', 'es3');

/**
 * Initializes Symbol.iterator (if it's not already defined) and adds a
 * Symbol.iterator property to the Array prototype.
 */
// TODO(rishipal): Remove this function
$jscomp.initSymbolIterator = function() {};

$jscomp.polyfill('Symbol.iterator', function(orig) {
  if (orig) return orig;  // no polyfill needed

  var symbolIterator = Symbol('Symbol.iterator');

  // Polyfill 'Symbol.iterator' onto Array and the various TypedArray* objects.
  // This array uses strings to index into $jscomp.global because the TypedArray
  // objects are present in IE11 but not on older browsers. Using bracket access
  // saves code size compared to `typeof Int8Array === 'function' && Int8Array`.
  var /** !Array */ arrayLikes = [
    'Array',
    // List taken from https://tc39.es/ecma262/#sec-typedarray-objects.
    // The BigInt*Arrays are intentionally omitted because they are only present
    // in browsers where Symbol is fully supported.
    'Int8Array', 'Uint8Array', 'Uint8ClampedArray', 'Int16Array', 'Uint16Array',
    'Int32Array', 'Uint32Array', 'Float32Array', 'Float64Array'
  ];

  for (var i = 0; i < arrayLikes.length; i++) {
    var ArrayLikeCtor = /** @type {*} */ ($jscomp.global[arrayLikes[i]]);
    if (typeof ArrayLikeCtor === 'function' &&
        typeof ArrayLikeCtor.prototype[symbolIterator] != 'function') {
      $jscomp.defineProperty(ArrayLikeCtor.prototype, symbolIterator, {
        configurable: true,
        writable: true,
        /**
         * @this {IArrayLike}
         * @return {!IteratorIterable}
         */
        value: function() {
          return $jscomp.iteratorPrototype($jscomp.arrayIteratorImpl(this));
        }
      });
    }
  }
  return symbolIterator;
}, 'es6', 'es3');

/**
 * Initializes Symbol.asyncIterator (if it's not already defined)
 */
// TODO(rishipal): Remove this function
$jscomp.initSymbolAsyncIterator = function() {};

$jscomp.polyfill('Symbol.asyncIterator', function(orig) {
  if (orig) {
    return orig;
  }
  return Symbol('Symbol.asyncIterator');
}, 'es9', 'es3');

/**
 * Returns an iterator with the given `next` method.  Passing
 * all iterators through this function allows easily extending
 * the definition of `%IteratorPrototype%` if methods are ever
 * added to it in the future.
 *
 * @param {function(this: Iterator): T} next
 * @return {!IteratorIterable}
 * @template T
 */
$jscomp.iteratorPrototype = function(next) {
  var iterator = {next: next};
  /**
   * @this {IteratorIterable}
   * @return {!IteratorIterable}
   */
  iterator[Symbol.iterator] = function() {
    return this;
  };
  return /** @type {!IteratorIterable} */ (iterator);
};