Js判斷CSS文件加載完畢的具體實(shí)現(xiàn)
要判斷這個(gè) CSS 文件是否加載完畢,各個(gè)瀏覽器的做法差異比較大,這次要說IE瀏覽器做的不錯(cuò),我們可以直接通過onload方法來處理CSS加載完成以后的處理:
// 代碼節(jié)選至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!
}
}
很遺憾,這次在其他的瀏覽器中,想判斷CSS是否加載完成就不是那么方便了,F(xiàn)F,webkit可以通過node.sheet.cssRules屬性是否存在來判斷是否加載完畢。而且需要使用setTimeout間隔事件輪詢:
// 代碼節(jié)選至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給出的完整的處理是這樣的:
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);
}
}
// 我的動(dòng)態(tài)創(chuàng)建LINK函數(shù)
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的代碼的時(shí)候,我立刻想起了我看到Diego Perini的另一個(gè)解決方案:
/*
* 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.dhdzp.com * 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);
})();
}
其實(shí),如果你讀過jQuery的domready事件的判斷的代碼,原理也類似。也是通過setTimeout輪詢的方式來判斷DOM節(jié)點(diǎn)是否加載完畢。
還有,F(xiàn)ackbook則是通過在動(dòng)態(tài)創(chuàng)建的CSS樣式中包含一個(gè)固定的樣式,例如#loadcssdom,loadcssdom就是一個(gè)高度為1px樣式。然后動(dòng)態(tài)創(chuàng)建一個(gè)DOM對(duì)象,添加這個(gè)loadcssdom樣式。然后也是setTimeout輪詢loadcssdo是否已經(jīng)有1px的高度了。這個(gè)處理方式的解決方案,大家可以下《CSSP: Loading CSS with Javascript – and getting an onload callback.》
而《JavaScript Patterns》的作者Stoyan則在他的博客里,比較詳細(xì)的說明了《When is a stylesheet really loaded?》。
看完了這些,你可能會(huì)感嘆:汗,判斷CSS是否加載完畢,目前還真不是那么容易!其實(shí)我這里算是一個(gè)拋磚引玉,因?yàn)殚_發(fā)中,除了動(dòng)態(tài)加載CSS,我們還要?jiǎng)討B(tài)加載JavaScript,動(dòng)態(tài)加載HTML的操作,有空我也會(huì)寫關(guān)于動(dòng)態(tài)加載JavaScript的相關(guān)內(nèi)容,不過在那之前,我建議你看看這些:
《ensure – Ensure JavaScripts/HTML/CSS are loaded on-demand when needed》,這個(gè)庫是專門處理動(dòng)態(tài)加載HTML,CSS,JavaScript的。就像作者介紹的那樣:
ensure is a tiny JavaScript library that provides a handy function ensure which allows you to load JavaScript, HTML, CSS on-demand, and then execute your code. ensure www.dhdzp.com ensures that the relevant JavaScript and HTML snippets are already in the browser DOM before executing your code that uses them.
《Tell CSS that JavaScript is available ASAP》
看完這個(gè)后,你可能就不會(huì)糾結(jié):When you're styling parts of a web page that will look and work differently depending on whether JavaScript is available or not。
好了,這次就說這么多了,希望對(duì)對(duì)大家的開發(fā)和學(xué)習(xí)有幫助!
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