使用postMessage来模拟setImmediate

setImmediate.js

  // We use setImmediate or postMessage for our future callback.
  var setImmediate = window.msSetImmediate;

  // Use post message to emulate setImmediate.
  if (!setImmediate) {
    var setImmediateQueue = [];
    var sentinel = String(Math.random());
    window.addEventListener('message', function(e) {
      if (e.data === sentinel) {
        var queue = setImmediateQueue;
        setImmediateQueue = [];
        queue.forEach(function(func) {
          func();
        });
      }
    });
    setImmediate = function(func) {
      setImmediateQueue.push(func);
      window.postMessage(sentinel, '*');
    };
  }