postMessage实现跨文档消息传输

在HTML5中新增了postMessage方法，postMessage可以实现跨文档消息传输（Cross Document Messaging），Internet Explorer 8, Firefox 3, Opera 9, Chrome 3和 Safari 4都支持postMessage。

/*
 * In window A's scripts, with A being on <http://example.com:8080>:
 */
var popup = window.open(...popup details...);
// When the popup has fully loaded, if not blocked by a popup blocker:
// This does nothing, assuming the window hasn't changed its location.
popup.postMessage("The user is 'bob' and the password is 'secret'",
"https://secure.example.net");
// This will successfully queue a message to be sent to the popup, assuming
// the window hasn't changed its location.
function receiveMessage(event)
{
  // Do we trust the sender of this message?  (might be
  // different from what we originally opened, for example).
  if (event.origin !== "http://example.org") return;
  // event.source is popup
  // event.data is "hi there yourself!  the secret response is: rheeeeet!"
}
window.addEventListener("message", receiveMessage, false);

可以通过绑定window的message事件来监听发送跨文档消息传输内容

[color=red]setTimeout经常被用来做网页上的定时器，允许为它指定一个毫秒数作为间隔执行的时间。当被启动的程序需要在非常短的时间内运行，我们就会给她指定一个很小的时间数，或者需要马上执行的话，我们甚至把这个毫秒数设置为0，但事实上，setTimeout有一个最小执行时间，当指定的时间小于该时间时，浏览器会用最小允许的时间作为setTimeout的时间间隔，也就是说即使我们把setTimeout的毫秒数设置为0，被调用的程序也没有马上启动。
postMessage实现无延迟的setTimeout基本思路是：将要调用的函数加入数组中，并马上向自己所在的窗口发一个消息，对窗口添加了接收消息事件，所以窗口马上就收到了该消息，接着就将之前数组中保存的函数弹出并执行。也就是绑定window窗体message事件去侦听这个事件。

// BEGIN implementation of setZeroTimeout
// Only add setZeroTimeout to the window object, and hide everything
// else in a closure.
(function() {
	var timeouts = [];
	var messageName = "zero-timeout-message";
	// Like setTimeout, but only takes a function argument.  There's
	// no time argument (always zero) and no arguments (you have to
	// use a closure).
	function setZeroTimeout(fn) {
		timeouts.push(fn);
		window.postMessage(messageName, "*");
	}
	function handleMessage(event) {
		if (event.source == window && event.data == messageName) {
			event.stopPropagation();
			if (timeouts.length> 0) {
				var fn = timeouts.shift();
				fn();
			}
		}
	}
	window.addEventListener("message", handleMessage, true);
	// Add the one thing we want added to the window object.
	window.setZeroTimeout = setZeroTimeout;
})();

外部调用方法来触发事件，此时触发内部message事件绑定handleMessage方法。

window.setZeroTimeout(function(){})

参考：
https://developer.mozilla.org/en/DOM/window.postMessage
http://blog.tugai.net/2010/03/27/postmessage-settimeout/