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如何判断css是否加载完成

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09/05
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要判断这个 CSS 文件是否加载完毕，各个浏览器的做法差异比较大，这次要说IE浏览器做的不错，我们可以直接通过onload方法来处理CSS加载完成以后的处理：

// 代码节选至seajs
function styleOnload(node, callback) {
// for IE6-9 and Opera
if (node.attachEvent) {
node.attachEvent('onload', callback);
// NOTICE:
// 1. "onload" will be fired in IE6-9 when the file is 404, but in
// this situation, Opera does nothing, so fallback to timeout.
// 2. "onerror" doesn't fire in any browsers!
}
}

很遗憾，这次在其他的浏览器中，想判断CSS是否加载完成就不是那么方便了，FF,webkit可以通过node.sheet.cssRules属性是否存在来判断是否加载完毕。而且需要使用setTimeout间隔事件轮询

// 代码节选至seajs
function poll(node, callback) {
if (callback.isCalled) {
return;
}
var isLoaded = false;
if (/webkit/i.test(navigator.userAgent)) {//webkit
if (node['sheet']) {
isLoaded = true;
}
}
// for Firefox
else if (node['sheet']) {
try {
if (node['sheet'].cssRules) {
isLoaded = true;
}
} catch (ex) {
// NS_ERROR_DOM_SECURITY_ERR
if (ex.code === 1000) {
isLoaded = true;
}
}
}
if (isLoaded) {
// give time to render.
setTimeout(function() {
callback();
}, 1);
}
else {
setTimeout(function() {
poll(node, callback);
}, 1);
}
} setTimeout(function() {
poll(node, callback);
}, 0);

SeaJS给出的完整的处理是这样的

function styleOnload(node, callback) {
// for IE6-9 and Opera
if (node.attachEvent) {
node.attachEvent('onload', callback);
// NOTICE:
// 1. "onload" will be fired in IE6-9 when the file is 404, but in
// this situation, Opera does nothing, so fallback to timeout.
// 2. "onerror" doesn't fire in any browsers!
}
// polling for Firefox, Chrome, Safari
else {
setTimeout(function() {
poll(node, callback);
}, 0); // for cache
}
}
function poll(node, callback) {
if (callback.isCalled) {
return;
}
var isLoaded = false;
if (/webkit/i.test(navigator.userAgent)) {//webkit
if (node['sheet']) {
isLoaded = true;
}
}
// for Firefox
else if (node['sheet']) {
try {
if (node['sheet'].cssRules) {
isLoaded = true;
}
} catch (ex) {
// NS_ERROR_DOM_SECURITY_ERR
if (ex.code === 1000) {
isLoaded = true;
}
}
}
if (isLoaded) {
// give time to render.
setTimeout(function() {
callback();
}, 1);
}
else {
setTimeout(function() {
poll(node, callback);
}, 1);
}
}
// 我的动态创建LINK函数
function createLink(cssURL,lnkId,charset,media){
var head = document.getElementsByTagName('head')[0],
linkTag = null; if(!cssURL){
return false;
} linkTag = document.createElement('link');
linkTag.setAttribute('id',(lnkId || 'dynamic-style'));
linkTag.setAttribute('rel','stylesheet');
linkTag.setAttribute('charset',(charset || 'utf-8'));
linkTag.setAttribute('media',(media||'all'));
linkTag.setAttribute('type','text/css');
linkTag.href = cssURL; head.appendChild(linkTag);
}
function loadcss(){
var styleNode = createLink('/wp-content/themes/BlueNight/style.css'); styleOnload(styleNode,function(){
alert("loaded");
});
}

在看到seajs的代码的时候，我立刻想起了我看到Diego Perini的另一个解决方案

/*
* Copyright (C) 2010 Diego Perini
* All rights reserved.
*
* cssready.js - CSS loaded/ready state notification
*
* Author: Diego Perini <diego.perini at gmail com>
* Version: 0.1
* Created: 20100616
* Release: 20101104
*
* License:
* http://www.jb51.net * Download:
* http://javascript.nwbox.com/cssready/cssready.js
*/
function cssReady(fn, link) {
var d = document,
t = d.createStyleSheet,
r = t ? 'rules' : 'cssRules',
s = t ? 'styleSheet' : 'sheet',
l = d.getElementsByTagName('link');
// passed link or last link node
link || (link = l[l.length - 1]);
function check() {
try {
return link && link[s] && link[s][r] && link[s][r][0];
} catch(e) {
return false;
}
}
(function poll() {
check() && setTimeout(fn, 0) || setTimeout(poll, 100);
})();
}

其实，如果你读过jQuery的domready事件的判断的代码，原理也类似。也是通过setTimeout轮询的方式来判断DOM节点是否加载完毕。