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javascript异步编程

　　本文标签：异步编程

<!doctype html> 
<html lang="en"> 
<head> 
<title>Async performance test</title> 
<meta charset="gb2312"> 
<style> 
pre { 
background-color: #eeeeee; 
padding: 20px; 
} 
div.test { 
margin: 20px; 
padding: 10px; 
border: solid black 1px; 
} 
</style> 
</head> 
<body> 
<div class="test"> 
<h3>setTimeout (slow, takes about 10 sec)</h3> 
<pre class="source"> 
function async(callback) { 
setTimeout(callback, 0); 
} 
</pre> 
<p> 
<input type="button" value="run" onclick="runtest(this.parentNode.parentNode)"> 
</P> 
</div>

<div class="test"> 
<h3>img.onerror (data:uri)</h3> 
<pre class="source"> 
function async(callback) { 
var img = new Image; 
img.addEventListener(error, callback, false); 
img.src = data:,foo; 
} 
</pre> 
<p> 
<input type="button" value="run" onclick="runtest(this.parentNode.parentNode)"> 
</P> 
</div>

<div class="test"> 
<h3>script.onreadystatechange</h3> 
<pre class="source"> 
function async(callback) { 
var script = document.createElement("script"); 
script.type = "text/javascript"; 
script.src = "javascript:"; 
script.onreadystatechange = function () { 
document.body.removeChild(script); 
callback(); 
} 
document.body.appendChild(script); 
} 
</pre> 
<p> 
<input type="button" value="run" onclick="runtest(this.parentNode.parentNode)"> 
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</div>

<div class="test"> 
<h3>script.onload (data:uri)</h3> 
<pre class="source"> 
function async(callback) { 
var script = document.createElement(script); 
script.onload = function() { 
document.body.removeChild(script); 
callback(); 
} 
script.src = data:text/javascript,; 
document.body.appendChild(script); 
} 
</pre> 
<p> 
<input type="button" value="run" onclick="runtest(this.parentNode.parentNode)"> 
</P> 
</div>

<div class="test"> 
<h3>xhr.onreadystatechange (data:text/plain,foo)</h3> 
<pre class="source"> 
function async(callback) { 
var xhr = new XMLHttpRequest; 
xhr.open(GET,data:text/plain,foo,true); 
xhr.onreadystatechange = function() { 
xhr.onreadystatechange = null; 
callback(); 
}; 
xhr.send(null); 
} 
</pre> 
<p> 
<input type="button" value="run" onclick="runtest(this.parentNode.parentNode)"> 
</P> 
</div>

<div class="test"> 
<h3>self.postMessage</h3> 
<pre class="source"> 
function async(callback) { 
var n = ++async.count; 
window.addEventListener(message,function(e){ 
if (e.data == n) { 
window.removeEventListener(message, arguments.callee,false); 
callback(); 
} 
},false); 
window.postMessage(n, location.protocol + "//" + location.host); 
} 
async.count = 0; 
</pre> 
<p> 
<input type="button" value="run" onclick="runtest(this.parentNode.parentNode)"> 
</P> 
</div>

var t = new Date, n = 1000, i = 0, flag = true; 
try { 
test(); 
} catch (e) {} 
setTimeout(function() {if (flag) p.innerHTML = failed; flag = false}, 200);

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