JavaScript 模拟后台任务

读书笔记，请勿转载，发布，产权不归我所有，归以前作者所有，我只是做读书笔记。

/*!
 * Copyright 2015 Google Inc. All rights reserved.
 *
 * 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.
 */
 
/*
 * @see https://developers.google.com/web/updates/2015/08/using-requestidlecallback
 */
window.requestIdleCallback = window.requestIdleCallback ||
  function (cb) {
    var start = Date.now();
    return setTimeout(function () {
      cb({ 
        didTimeout: false,
        timeRemaining: function () {
          return Math.max(0, 50 - (Date.now() - start));
        }
      });
    }, 1);
  }

window.cancelIdleCallback = window.cancelIdleCallback ||
  function (id) {
    clearTimeout(id);
  }