转-流框架中DOMContentLoaded事件的实现
转自:http://www.ipmtea.net/jquery/201009/27_308.html
//PS: 部分代码仅供参考,jquery的实现似乎有bug
//参考最新jquery实现
在实际应用中,我们经常会遇到这样的场景,当页面加载完成后去做一些事情:绑定事件、DOM操作某些结点等。原来比较常用的是window的onload事件,而该事件的实际效果是:当页面解析/DOM树建立完成,并完成了诸如图片、脚本、样式表甚至是iframe中所有资源的下载后才触发的。这对于很多实际的应用而言有点太“迟”了,比较影响用户体验。为了解决这个问题,FF中便增加了一个DOMContentLoaded方法,与onload相比,该方法触发的时间更早,它是在页面的DOM内容加载完成后即触发,而无需等待其他资源的加载。Webkit引擎从版本525(Webkit nightly 1/2008:525+)开始也引入了该事件,Opera中也包含该方法。到目前为止主流的IE仍然没有要添加的意思。虽然IE下没有,但总是有解决办法的,下文对比了一下几大主流框架对于该事件的兼容性版本实现方案,涉及的框架包括:
- Prototype
- jQeury
- moontools
- dojo
- yui
- ext
一、Prototype
实现代码
- (function() {
- /* Support for the DOMContentLoaded event is based on work by Dan Webb,
- Matthias Miller, Dean Edwards and John Resig. */
- var timer;
- function fireContentLoadedEvent() {
- if (document.loaded) return;
- if (timer) window.clearInterval(timer);
- document.fire("dom:loaded");
- document.loaded = true;
- }
- if (document.addEventListener) {
- if (Prototype.Browser.WebKit) {
- timer = window.setInterval(function() {
- if (/loaded|complete/.test(document.readyState))
- fireContentLoadedEvent();
- }, 0);
- Event.observe(window, "load", fireContentLoadedEvent);
- } else {
- document.addEventListener("DOMContentLoaded",
- fireContentLoadedEvent, false);
- }
- } else {
- document.write("<"+"script id=__onDOMContentLoaded defer src=//:><\/script>");
- $("__onDOMContentLoaded").onreadystatechange = function() {
- if (this.readyState == "complete") {
- this.onreadystatechange = null;
- fireContentLoadedEvent();
- }
- };
- }
- })();
实现思路如下:
1、如果是webkit则轮询document的readyState属性,如果该属性的值为loaded或complete则触发DOMContentLoaded事件,为保险起见,将该事件注册到window.onload上。
2、如果是FF则直接注册DOMContentLoaded事件。
3、如果是IE则使用document.write往页面中加入一个script元素,并设置defer属性,最后是把该脚本的加载完成视作DOMContentLoaded事件来触发。
该实现方式的问题主要有两点:第一、通过document.write写script并设置defer的方法在页面包含iframe的情况下,会等到iframe内的内容加载完后才触发,这与onload没有太大的区别;第二、Webkit在525以上的版本引入了DOMContentLoaded方法,因此在这些版本中无需再通过轮询来实现,可以优化。
二、jQuery
- function bindReady(){
- if ( readyBound ) return;
- readyBound = true;
- // Mozilla, Opera and webkit nightlies currently support this event
- if ( document.addEventListener ) {
- // Use the handy event callback
- document.addEventListener( "DOMContentLoaded", function(){
- document.removeEventListener( "DOMContentLoaded", arguments.callee, false );
- jQuery.ready();
- }, false );
- // If IE event model is used
- } else if ( document.attachEvent ) {
- // ensure firing before onload,
- // maybe late but safe also for iframes
- document.attachEvent("onreadystatechange", function(){
- if ( document.readyState === "complete" ) {
- document.detachEvent( "onreadystatechange", arguments.callee );
- jQuery.ready();
- }
- });
- // If IE and not an iframe
- // continually check to see if the document is ready
- if ( document.documentElement.doScroll && typeof window.frameElement === "undefined" )
- (function(){
- if ( jQuery.isReady ) return;
- try {
- // If IE is used, use the trick by Diego Perini
- // http://javascript.nwbox.com/IEContentLoaded/
- document.documentElement.doScroll("left");
- } catch( error ) {
- setTimeout( arguments.callee, 0 );
- return;
- }
- // and execute any waiting functions
- jQuery.ready();
- })();
- }
- // A fallback to window.onload, that will always work
- jQuery.event.add( window, "load", jQuery.ready );
- }
实现思路如下:
1、将Webkit与Firefox同等对待,都是直接注册DOMContentLoaded事件,但是由于Webkit是在525以上版本才引入的,因此存在兼容性的隐患。
2、对于IE,首先注册document的onreadystatechange事件,经测试,该方式与window.onload相当,依然会等到所有资源下载完毕后才触发。
3、之后,判断如果是IE并且页面不在iframe当中,则通过setTiemout来不断的调用documentElement的doScroll方法,直到调用成功则出触发DOMContentLoaded。1
jQuery对于IE的解决方案,使用了一种新的方法,该方法源自http://javascript.nwbox.com/IEContentLoaded/。它的原理是,在IE下,DOM的某些方法只有在DOM解析完成后才可以调用,doScroll就是这样一个方法,反过来当能调用doScroll的时候即是DOM解析完成之时,与prototype中的document.write相比,该方案可以解决页面有iframe时失效的问题。此外,jQuery似乎担心当页面处于iframe中时,该方法会失效,因此实现代码中做了判断,如果是在iframe中则通过document的onreadystatechange来实现,否则通过doScroll来实现。不过经测试,即使是在iframe中,doScroll依然有效。
三、Moontools
//最新版本
//1.4.5
(function(window, document){ var ready, loaded, checks = [], shouldPoll, timer, testElement = document.createElement('div'); var domready = function(){ clearTimeout(timer); if (ready) return; Browser.loaded = ready = true; document.removeListener('DOMContentLoaded', domready).removeListener('readystatechange', check); document.fireEvent('domready'); window.fireEvent('domready'); }; var check = function(){ for (var i = checks.length; i--;) if (checks[i]()){ domready(); return true; } return false; }; var poll = function(){ clearTimeout(timer); if (!check()) timer = setTimeout(poll, 10); }; document.addListener('DOMContentLoaded', domready); /**/ // doScroll technique by Diego Perini http://javascript.nwbox.com/IEContentLoaded/ // testElement.doScroll() throws when the DOM is not ready, only in the top window var doScrollWorks = function(){ try { testElement.doScroll(); return true; } catch (e){} return false; }; // If doScroll works already, it can't be used to determine domready // e.g. in an iframe if (testElement.doScroll && !doScrollWorks()){ checks.push(doScrollWorks); shouldPoll = true; } /**/ if (document.readyState) checks.push(function(){ var state = document.readyState; return (state == 'loaded' || state == 'complete'); }); if ('onreadystatechange' in document) document.addListener('readystatechange', check); else shouldPoll = true; if (shouldPoll) poll(); Element.Events.domready = { onAdd: function(fn){ if (ready) fn.call(this); } }; // Make sure that domready fires before load Element.Events.load = { base: 'load', onAdd: function(fn){ if (loaded && this == window) fn.call(this); }, condition: function(){ if (this == window){ domready(); delete Element.Events.load; } return true; } }; // This is based on the custom load event window.addEvent('load', function(){ loaded = true; }); })(window, document);
实现思路如下:
1、如果是IE则使用doScroll方法来实现。
2、如果是小于525版本的Webkit则通过轮询document.readyState来实现。
3、其他的(FF/Webkit高版/Opera)则直接注册DOMContentLoaded事件。
Moontools的实现方案prototype和jQeury中的综合体,对webkit做了版本判断则使得该方案更加的健壮。在doScroll的实现方面,与jQuery相比,这里是新建了一个div元素,并且在使用完毕后进行销毁,而jQuery则直接使用了documentElement的doScroll来检测,更简单高效一些。
四、Dojo
- // START DOMContentLoaded
- // Mozilla and Opera 9 expose the event we could use
- if(document.addEventListener){
- // NOTE:
- // due to a threading issue in Firefox 2.0, we can't enable
- // DOMContentLoaded on that platform. For more information, see:
- // http://trac.dojotoolkit.org/ticket/1704
- if(dojo.isOpera || dojo.isFF >= 3 || (dojo.isMoz && dojo.config.enableMozDomContentLoaded === true)){
- document.addEventListener("DOMContentLoaded", dojo._loadInit, null);
- }
- // mainly for Opera 8.5, won't be fired if DOMContentLoaded fired already.
- // also used for Mozilla because of trac #1640
- window.addEventListener("load", dojo._loadInit, null);
- }
- if(dojo.isAIR){
- window.addEventListener("load", dojo._loadInit, null);
- }else if(/(WebKit|khtml)/i.test(navigator.userAgent)){ // sniff
- dojo._khtmlTimer = setInterval(function(){
- if(/loaded|complete/.test(document.readyState)){
- dojo._loadInit(); // call the onload handler
- }
- }, 10);
- }
- // END DOMContentLoaded
- }
- (function(){
- var _w = window;
- var _handleNodeEvent = function(/*String*/evtName, /*Function*/fp){
- // summary:
- // non-destructively adds the specified function to the node's
- // evtName handler.
- // evtName: should be in the form "onclick" for "onclick" handlers.
- // Make sure you pass in the "on" part.
- var oldHandler = _w[evtName] || function(){};
- _w[evtName] = function(){
- fp.apply(_w, arguments);
- oldHandler.apply(_w, arguments);
- };
- };
- if(dojo.isIE){
- // for Internet Explorer. readyState will not be achieved on init
- // call, but dojo doesn't need it however, we'll include it
- // because we don't know if there are other functions added that
- // might. Note that this has changed because the build process
- // strips all comments -- including conditional ones.
- if(!dojo.config.afterOnLoad){
- document.write('<SCR'+'IPT ?onreadystatechange="if(this.readyState==\'complete\'){' + dojo._scopeName + '._loadInit();}" + ? src="//:" defer>'
- + '</SCR'+'IPT>'
- );
- }
- try{
- document.namespaces.add("v","urn:schemas-microsoft-com:vml");
- document.createStyleSheet().addRule("v\\:*", "behavior:url(#default#VML)");
- }catch(e){}
- }
- // FIXME: dojo.unloaded requires dojo scope, so using anon function wrapper.
- _handleNodeEvent("onbeforeunload", function() { dojo.unloaded(); });
- _handleNodeEvent("onunload", function() { dojo.windowUnloaded(); });
- })();
实现思路如下:
1、如果是Opera或FF3以上版本则直接注册DOMContentLoaded<事件,为保险起见,同时也注册了window.onload事件。/li>
2、对于webkit则通过轮询document.readyState来实现。
3、如果是Air则只注册widnow.onload事件。
4、如果是IE则通过往页面写带defer属性的script并注册其onreadystatechange事件来实现。
Dojo在IE下的实现方案同样无法解决iframe的问题,而由于在FF2 下会有一个非常奇怪的Bug,因此默认只在FF3以上版本上使用DOMContentLoaded事件,同时又给了一个配置-dojo.config.enableMozDomContentLoaded,如果在FF下将该配置设置为true则依然会使用DOMContentLoaded来实现,这一点充分考虑到了灵活性。对于webkit的实现,与prototype一样有优化的空间。
五、YUI
- /*! DOMReady: based on work by: Dean Edwards/John Resig/Matthias Miller */
- // Internet Explorer: use the readyState of a defered script.
- // This isolates what appears to be a safe moment to manipulate
- // the DOM prior to when the document's readyState suggests
- // it is safe to do so.
- if (EU.isIE) {
- // Process onAvailable/onContentReady items when the
- // DOM is ready.
- YAHOO.util.Event.onDOMReady(
- YAHOO.util.Event._tryPreloadAttach,
- YAHOO.util.Event, true);
- var n = document.createElement('p');
- EU._dri = setInterval(function() {
- try {
- // throws an error if doc is not ready
- n.doScroll('left');
- clearInterval(EU._dri);
- EU._dri = null;
- EU._ready();
- n = null;
- } catch (ex) {
- }
- }, EU.POLL_INTERVAL);
- // The document's readyState in Safari currently will
- // change to loaded/complete before images are loaded.
- } else if (EU.webkit && EU.webkit < 525) {
- EU._dri = setInterval(function() {
- var rs=document.readyState;
- if ("loaded" == rs || "complete" == rs) {
- clearInterval(EU._dri);
- EU._dri = null;
- EU._ready();
- }
- }, EU.POLL_INTERVAL);
- // FireFox and Opera: These browsers provide a event for this
- // moment. The latest WebKit releases now support this event.
- } else {
- EU._simpleAdd(document, "DOMContentLoaded", EU._ready);
- }
- /////////////////////////////////////////////////////////////
- EU._simpleAdd(window, "load", EU._load);
- EU._simpleAdd(window, "unload", EU._unload);
- EU._tryPreloadAttach();
- })();
实现思路与Moontools的一致,不再赘诉。
六、EXT
- function initDocReady(){
- var COMPLETE = "complete";
- docReadyEvent = new Ext.util.Event();
- if (Ext.isGecko || Ext.isOpera) {
- DOC.addEventListener(DOMCONTENTLOADED, fireDocReady, false);
- } else if (Ext.isIE){
- DOC.write("<S"+'CRIPT id=" + IEDEFERED + " src="/'+'/:" defer="defer"></S'+"CRIPT>");
- DOC.getElementById(IEDEFERED).onreadystatechange = function(){
- if(this.readyState == COMPLETE){
- fireDocReady();
- }
- };
- } else if (Ext.isWebKit){
- docReadyProcId = setInterval(function(){
- if(DOC.readyState == COMPLETE) {
- fireDocReady();
- }
- }, 10);
- }
- // no matter what, make sure it fires on load
- E.on(WINDOW, "load", fireDocReady);
- };
实现思路与Dojo的一致,不再赘诉。
总结
总结各大主流框架的做法,写了以下这个版本。主要是尽量的做到优化并考虑到FF2下的Bug,提供一个是否使用DOMContentLoaded的开关配置。
- /*
- * 注册浏览器的DOMContentLoaded事件
- * @param { Function } onready [必填]在DOMContentLoaded事件触发时需要执行的函数
- * @param { Object } config [可选]配置项
- */
- function onDOMContentLoaded(onready,config){
- //浏览器检测相关对象,在此为节省代码未实现,实际使用时需要实现。
- //var Browser = {};
- //设置是否在FF下使用DOMContentLoaded(在FF2下的特定场景有Bug)
- this.conf = {enableMozDOMReady:true};
- if( config )
- for( var p in config)
- this.conf[p] = config[p];
- var isReady = false;
- function doReady(){
- if( isReady ) return;
- //确保onready只执行一次
- isReady = true;
- onready();
- }
- /*IE*/
- if( Browser.ie ){
- (function(){
- if ( isReady ) return;
- try {
- document.documentElement.doScroll("left");
- } catch( error ) {
- setTimeout( arguments.callee, 0 );
- return;
- }
- doReady();
- })();
- window.attachEvent('onload',doReady);
- }
- /*Webkit*/
- else if (Browser.webkit && Browser.version < 525){
- (function(){
- if( isReady ) return;
- if (/loaded|complete/.test(document.readyState))
- doReady();
- else
- setTimeout( arguments.callee, 0 );
- })();
- window.addEventListener('load',doReady,false);
- }
- /*FF Opera 高版webkit 其他*/
- else{
- if( !Browser.ff || Browser.version != 2 || this.conf.enableMozDOMReady)
- document.addEventListener( "DOMContentLoaded", function(){
- document.removeEventListener( "DOMContentLoaded", arguments.callee, false );
- doReady();
- }, false );
- window.addEventListener('load',doReady,false);
- }
- }