nos*_*tio 5 javascript html5 message asynchronous timeout
显然,使用window.postMessage是在所有现代浏览器中对异步javascript回调进行排队的首选方法window.setTimeout(fn, 0).我在window.postMessage和MessagePort.postMessage之间找不到类似的比较(使用相同的MessageChannel异步发送和接收消息).有没有人见过或做过任何时间？MessagePort.postMessage是否可以用于此目的(如果可用)？
[EDITED] MessagePort.postMessage确实为此工作,但window.postMessage仍然是一种优先的方式,IMO(见我的回答).
[更新]添加了对setImmediate和JSFiddle的测试。相关的，有一个跨浏览器实现的setImmediate，并尽快库使用Q的承诺分辨率/拒绝。
我继续进行了一些时间安排，使用了David Baron的代码的修改版本，结果如下：
setTimeoutMC-使用MessageChannel
setTimeoutPM-使用window.postMessage
setTimeout(0)-使用setTimer
IE10：
2000 iterations of setTimeoutMC took 126 milliseconds.
2000 iterations of setTimeoutPM took 190 milliseconds.
2000 iterations of setTimeout(0) took 7986 milliseconds.
Chrome v29.0.1547.66：
2000 iterations of setTimeoutMC took 144 milliseconds.
2000 iterations of setTimeoutPM took 81 milliseconds.
2000 iterations of setTimeout(0) took 10589 milliseconds.
显然，window.postMessage是这里的赢家（考虑到它对现有跨浏览器的支持水平）。较为宽松的是window.setTimeout(fn, 0)，应尽可能避免。
码：
<!DOCTYPE html>
<html>
<head>
<!-- http://stackoverflow.com/q/18826570/1768303 -->
<!-- based on http://dbaron.org/log/20100309-faster-timeouts -->
<!-- requires IE10 or Chrome. Firefox doesn't support MessageChannel yet -->
<title></title>
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<script type="text/javascript">
// setTimeoutMC via MessageChannel
(function () {
"use strict";
var i = 0;
var timeouts = {};
var setApiName = "setTimeoutMC";
var clearApiName = "clearTimeoutMC";
var channel = new MessageChannel();
function post(fn) {
if (i === 0x100000000) // max queue size
i = 0;
if (++i in timeouts)
throw new Error(setApiName + " queue overflow.");
timeouts[i] = fn;
channel.port2.postMessage(i);
return i;
}
channel.port1.onmessage = function (ev) {
var id = ev.data;
var fn = timeouts[id];
if (fn) {
delete timeouts[id];
fn();
}
}
function clear(id) {
delete timeouts[id];
}
channel.port1.start();
channel.port2.start();
window[setApiName] = post;
window[clearApiName] = clear;
})();
// setTimeoutPM via window.postMessage
(function () {
"use strict";
var i = 0;
var timeouts = {};
var setApiName = "setTimeoutPM";
var clearApiName = "clearTimeoutPM";
var messageName = setApiName + new Date().getTime();
function post(fn) {
if (i === 0x100000000) // max queue size
i = 0;
if (++i in timeouts)
throw new Error(setApiName + " queue overflow.");
timeouts[i] = fn;
window.postMessage({ type: messageName, id: i }, "*");
return i;
}
function receive(ev) {
if (ev.source !== window)
return;
var data = ev.data;
if (data && data instanceof Object && data.type === messageName) {
ev.stopPropagation();
var id = ev.data.id;
var fn = timeouts[id];
if (fn) {
delete timeouts[id];
fn();
}
}
}
function clear(id) {
delete timeouts[id];
}
window.addEventListener("message", receive, true);
window[setApiName] = post;
window[clearApiName] = clear;
})();
// timing
function runtest() {
var output = document.getElementById("output");
var outputText = document.createTextNode("");
output.appendChild(outputText);
function printOutput(line) {
outputText.data += line + "\n";
}
var n = 2000;
var i = 0;
var startTime = Date.now();
setTimeoutMC(testMC);
function testMC() {
if (++i === n) {
var endTime = Date.now();
printOutput(n + " iterations of setTimeoutMC took " + (endTime - startTime) + " milliseconds.");
i = 0;
startTime = Date.now();
setTimeoutPM(testPM, 0);
} else {
setTimeoutMC(testMC);
}
}
function testPM() {
if (++i === n) {
var endTime = Date.now();
printOutput(n + " iterations of setTimeoutPM took " + (endTime - startTime) + " milliseconds.");
i = 0;
startTime = Date.now();
setTimeout(test, 0);
} else {
setTimeoutPM(testPM);
}
}
function test() {
if (++i === n) {
var endTime = Date.now();
printOutput(n + " iterations of setTimeout(0) took " + (endTime - startTime) + " milliseconds.");
}
else {
setTimeout(test, 0);
}
}
}
</script>
</head>
<body onload="runtest()">
<pre id="output"></pre>
</body>
</html>
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