javascript异步编程_javascript技巧

setTimeout (slow, takes about 10 sec)

function async(callback) {
setTimeout(callback, 0);
}

img.onerror (data:uri)

function async(callback) {
var img = new Image;
img.addEventListener('error', callback, false);
img.src = 'data:,foo';
}

script.onreadystatechange

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);
}

script.onload (data:uri)

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);
}

xhr.onreadystatechange (data:text/plain,foo)

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);
}

self.postMessage

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;

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