setTimeout(0)对window.postMessage对MessagePort.postMessage
setTimeout(0)对window.postMessage对MessagePort.postMessage
提问于 2013-09-16 11:13:52
显然，使用window.postMessage是在所有现代浏览器上通过window.setTimeout(fn, 0)对异步javascript回调进行排队的优选方式。我无法在window.postMessage和MessagePort.postMessage之间找到类似的比较(使用相同的MessageChannel异步发送和接收消息)。有人看到或做了什么时间吗？MessagePort.postMessage是否为此目的工作(在可用的情况下)？
编辑的 MessagePort.postMessage确实能做到这一点，但window.postMessage仍然是一种预先提出的方法，IMO (见我的答案)。
回答 1
Stack Overflow用户
回答已采纳
发布于 2013-09-16 16:30:56
UPDATE为setImmediate和JSFiddle添加了一个测试。与此相关的是，有一个跨浏览器实现 of setImmediate和ASAP库被问：用于承诺解决/拒绝。
我使用了修改后的大卫·巴伦密码版本，进行了一些计时，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(考虑到现有的跨浏览器对它的支持程度)。更宽松的是window.setTimeout(fn, 0)，应该尽可能避免。
代码：
<!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>页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/18826570
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