window.matchMedia = window.matchMedia ||(function(doc, undefined){var bool,docElem = doc.documentElement,refNode = docElem.firstElementChild || docElem.firstChild,//fakeBody required forfakeBody= doc.createElement_x('body'),div     = doc.createElement_x('div');div.id = 'mq-test-1';div.style.cssText = "position:absolute;top:-100em";fakeBody.style.background = "none";fakeBody.appendChild(div);return function(q){div.innerHTML= '-';docElem.insertBefore(fakeBody,refNode);bool= div.offsetWidth == 42;docElem.removeChild(fakeBody);return{ matches: bool, media: q };};
})(document);
//檢測是否支持mediaquery,檢測css是否有效的方法都差不多，創建一個元素應用該css后檢測元素寬度，然后清除該元素。
<pre name="code" class="css">.......
if( !!href &&isCSS && !parsedSheets[ href ] ){//selectivizr exposes css through the rawCssText expandoif(sheet.styleSheet &&sheet.styleSheet.rawCssText) {//sheet.styleSheet.rawCssText看不懂，原來是方便selectivizr和respond.js聯用，http://selectivizr.com/tests/respond///selectivizr的作用是CSS3 selectors forIE；約定將原csstext放在styleSheet的link上的擴展屬性rawCssText上；這里如果聯用selectivizr可以少次ajax請求translate(sheet.styleSheet.rawCssText, href, media );parsedSheets[href ] = true;}else {if((!/^([a-zA-Z:]*\/\/)/.test( href ) && !base)||href.replace( RegExp.$1, "").split( "/" )[0] ===win.location.host ){requestQueue.push({href:href,media:media});}}
}
.......

//把cross-domain/respond-proxy.html放到cdn上
//把cross-domain/respond.proxy.gif放到當前域服務器上
"http://externalcdn.com/respond-proxy.html"id="respond-proxy" rel="respond-proxy" />"/path/to/respond.proxy.gif" id="respond-redirect" rel="respond-redirect" />"/path/to/respond.proxy.js">

function checkFrameName() {varcssText;try{cssText= iframe.contentWindow.name;varnow = new Date().getTime(),useTime = now - initTime;alert('獲取css耗時:'+useTime + 'ms');}catch(e) { }if(cssText) {……//銷毀之前用于通信的iframe,后續回調callbackcallback(cssText);}else{win.setTimeout(checkFrameName,100);}
}
win.setTimeout(checkFrameName, 500);//500ms后確認內部iframe的name值是否傳遞過來，后續再更新當前viewport該用的css。

//prevent jumping of layout by hiding everything beforepainting 先將html移出可視區域外
var docEl =document.documentElement;docEl.style.marginLeft= '-32767px';//make sure it comes back after a while 異常處理，萬一獲取mediaquerycss失敗，重置回來
setTimeout(function (){docEl.style.marginTop = '';
},20000);……// return visibility after media queries are tested生效后重新可見
cssHelper.addListener('cssMediaQueriesTested', function() {//force repaint in IE by changing widthif(ua.ie) {docEl.style.width= '1px';}setTimeout(function() {docEl.style.width= ''; // undowidthdocEl.style.marginLeft= ''; // undohidevarnow = new Date().getTime();varuseTime = now - initTime;alert('mediaquery生效時間:'+useTime+'ms');},0);//remove this listener to prevent following executioncssHelper.removeListener('cssMediaQueriesTested',arguments.callee);
});

"stylesheet" type="text/css"media="screenand (max-width: 990px)" href="respond750.css&uuot;>
stylesheet"type="text/css" media="screen and(max-width: 1200px)"href="respond990.css">