Steve Souders写的异步加载脚本的同时保持顺序（提高前端性能）

通过《高性能网站建设进阶指南》收获很多！

特别是Steve Souders写的并行加载多个外部脚本函数，已经在项目中通用，速度真的提升了很多。

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方法调用时写法
function init(){//写脚本加载完成后执行的代码}EFWS.Script.loadScripts( ["http://ajax.googleapis.com/ajax/libs/jquery/1.4/jquery.min.js","script/miniSite.js"], init);

核心内容

if ( "undefined" == typeof(EFWS) || !EFWS ) {var EFWS = {};}EFWS.Script = {loadScript: function(url, onload) {EFWS.Script.loadScriptDomElement(url, onload);},loadScripts: function(aUrls, onload) {// first pass: see if any of the scripts are on a different domainvar nUrls = aUrls.length;var bDifferent = false;for ( var i = 0; i < nUrls; i++ ) {if ( EFWS.Script.differentDomain(aUrls[i]) ) {bDifferent = true;break;}}// pick the best loading functionvar loadFunc = EFWS.Script.loadScriptXhrInjection;if ( bDifferent ) {if ( -1 != navigator.userAgent.indexOf('Firefox') || -1 != navigator.userAgent.indexOf('Opera') ) {loadFunc = EFWS.Script.loadScriptDomElement;}else {loadFunc = EFWS.Script.loadScriptDocWrite;}}// second pass: load the scriptsfor ( var i = 0; i < nUrls; i++ ) {loadFunc(aUrls[i], ( i+1 == nUrls ? onload : null ), true);}},differentDomain: function(url) {if ( 0 === url.indexOf('http://') || 0 === url.indexOf('https://') ) {var mainDomain = document.location.protocol + "://" + document.location.host + "/";return ( 0 !== url.indexOf(mainDomain) );}return false;},loadScriptDomElement: function(url, onload) {var domscript = document.createElement('script');domscript.src = url;if ( onload ) {domscript.onloadDone = false;domscript.onload = function() { if ( !domscript.onloadDone ) {domscript.onloadDone = true; onload(); }};domscript.onreadystatechange = function() {if ( ( "loaded" === domscript.readyState || "complete" === domscript.readyState ) && !domscript.onloadDone ) {domscript.onloadDone = true;domscript.onload();}}}document.getElementsByTagName('head')[0].appendChild(domscript);},loadScriptDocWrite: function(url, onload) {document.write('<scr' + 'ipt src="' + url + '" type="text/javascript"></scr' + 'ipt>');if ( onload ) {// we can't tie it to the script's onload, so use window// thus, it doesn't fire as early as it might haveEFWS.addHandler(window, "load", onload);}},queuedScripts: new Array(),loadScriptXhrInjection: function(url, onload, bOrder) {var iQueue = EFWS.Script.queuedScripts.length;if ( bOrder ) {var qScript = { response: null, onload: onload, done: false };EFWS.Script.queuedScripts[iQueue] = qScript;}var xhrObj = EFWS.Script.getXHRObject();xhrObj.onreadystatechange = function() { if ( xhrObj.readyState == 4 ) {if ( bOrder ) {EFWS.Script.queuedScripts[iQueue].response = xhrObj.responseText;EFWS.Script.injectScripts();}else {var se = document.createElement('script');document.getElementsByTagName('head')[0].appendChild(se);se.text = xhrObj.responseText;if ( onload ) {onload();}}}};xhrObj.open('GET', url, true);xhrObj.send('');},injectScripts: function() {var len = EFWS.Script.queuedScripts.length;for ( var i = 0; i < len; i++ ) {var qScript = EFWS.Script.queuedScripts[i];if ( ! qScript.done ) {if ( ! qScript.response ) {// STOP! need to wait for this responsebreak;}else {var se = document.createElement('script');document.getElementsByTagName('head')[0].appendChild(se);se.text = qScript.response;if ( qScript.onload ) {qScript.onload();}qScript.done = true;}}}},getXHRObject: function() {var xhrObj = false;try {xhrObj = new XMLHttpRequest();}catch(e){var aTypes = ["Msxml2.XMLHTTP.6.0", "Msxml2.XMLHTTP.3.0", "Msxml2.XMLHTTP", "Microsoft.XMLHTTP"];var len = aTypes.length;for ( var i=0; i < len; i++ ) {try {xhrObj = new ActiveXObject(aTypes[i]);}catch(e) {continue;}break;}}finally {return xhrObj;}}};EFWS.addHandler = function(elem, type, func) {if ( elem.addEventListener ) {elem.addEventListener(type, func, false);}else if ( elem.attachEvent ) {elem.attachEvent("on" + type, func);}};