respond.js 是一个快速、轻量的 polyfill，用于为 IE6-8 以及其它不支持 CSS3 Media Queries 的浏览器提供媒体查询的 min-width 和 max-width 特性，实现响应式网页设计（Responsive Web Design）。

(function(w) {

  "use strict";

  w.matchMedia = w.matchMedia || function(doc, undefined) {

    var bool, docElem = doc.documentElement, refNode = docElem.firstElementChild || docElem.firstChild, fakeBody = doc.createElement("body"), div = doc.createElement("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 = '&shy;<style media="' + q + '"> #mq-test-1 { width: 42px; }</style>';

      docElem.insertBefore(fakeBody, refNode);

      bool = div.offsetWidth === 42;

      docElem.removeChild(fakeBody);

      return {

        matches: bool,

        media: q

      };

    };

  }(w.document);

})(this);



(function(w) {

  "use strict";

  var respond = {};

  w.respond = respond;

  respond.update = function() {};

  var requestQueue = [], xmlHttp = function() {

    var xmlhttpmethod = false;

    try {

      xmlhttpmethod = new w.XMLHttpRequest();

    } catch (e) {

      xmlhttpmethod = new w.ActiveXObject("Microsoft.XMLHTTP");

    }

    return function() {

      return xmlhttpmethod;

    };

  }(), ajax = function(url, callback) {

    var req = xmlHttp();

    if (!req) {

      return;

    }

    req.open("GET", url, true);

    req.onreadystatechange = function() {

      if (req.readyState !== 4 || req.status !== 200 && req.status !== 304) {

        return;

      }

      callback(req.responseText);

    };

    if (req.readyState === 4) {

      return;

    }

    req.send(null);

  }, isUnsupportedMediaQuery = function(query) {

    return query.replace(respond.regex.minmaxwh, "").match(respond.regex.other);

  };

  respond.ajax = ajax;

  respond.queue = requestQueue;

  respond.unsupportedmq = isUnsupportedMediaQuery;

  respond.regex = {

    media: /@media[^\{]+\{([^\{\}]*\{[^\}\{]*\})+/gi,

    keyframes: /@(?:\-(?:o|moz|webkit)\-)?keyframes[^\{]+\{(?:[^\{\}]*\{[^\}\{]*\})+[^\}]*\}/gi,

    comments: /\/\*[^*]*\*+([^/][^*]*\*+)*\//gi,

    urls: /(url\()['"]?([^\/\)'"][^:\)'"]+)['"]?(\))/g,

    findStyles: /@media *([^\{]+)\{([\S\s]+?)$/,

    only: /(only\s+)?([a-zA-Z]+)\s?/,

    minw: /\(\s*min\-width\s*:\s*(\s*[0-9\.]+)(px|em)\s*\)/,

    maxw: /\(\s*max\-width\s*:\s*(\s*[0-9\.]+)(px|em)\s*\)/,

    minmaxwh: /\(\s*m(in|ax)\-(height|width)\s*:\s*(\s*[0-9\.]+)(px|em)\s*\)/gi,

    other: /\([^\)]*\)/g

  };

  respond.mediaQueriesSupported = w.matchMedia && w.matchMedia("only all") !== null && w.matchMedia("only all").matches;

  if (respond.mediaQueriesSupported) {

    return;

  }

  var doc = w.document, docElem = doc.documentElement, mediastyles = [], rules = [], appendedEls = [], parsedSheets = {}, resizeThrottle = 30, head = doc.getElementsByTagName("head")[0] || docElem, base = doc.getElementsByTagName("base")[0], links = head.getElementsByTagName("link"), lastCall, resizeDefer, eminpx, getEmValue = function() {

    var ret, div = doc.createElement("div"), body = doc.body, originalHTMLFontSize = docElem.style.fontSize, originalBodyFontSize = body && body.style.fontSize, fakeUsed = false;

    div.style.cssText = "position:absolute;font-size:1em;width:1em";

    if (!body) {

      body = fakeUsed = doc.createElement("body");

      body.style.background = "none";

    }

    docElem.style.fontSize = "100%";

    body.style.fontSize = "100%";

    body.appendChild(div);

    if (fakeUsed) {

      docElem.insertBefore(body, docElem.firstChild);

    }

    ret = div.offsetWidth;

    if (fakeUsed) {

      docElem.removeChild(body);

    } else {

      body.removeChild(div);

    }

    docElem.style.fontSize = originalHTMLFontSize;

    if (originalBodyFontSize) {

      body.style.fontSize = originalBodyFontSize;

    }

    ret = eminpx = parseFloat(ret);

    return ret;

  }, applyMedia = function(fromResize) {

    var name = "clientWidth", docElemProp = docElem[name], currWidth = doc.compatMode === "CSS1Compat" && docElemProp || doc.body[name] || docElemProp, styleBlocks = {}, lastLink = links[links.length - 1], now = new Date().getTime();

    if (fromResize && lastCall && now - lastCall < resizeThrottle) {

      w.clearTimeout(resizeDefer);

      resizeDefer = w.setTimeout(applyMedia, resizeThrottle);

      return;

    } else {

      lastCall = now;

    }

    for (var i in mediastyles) {

      if (mediastyles.hasOwnProperty(i)) {

        var thisstyle = mediastyles[i], min = thisstyle.minw, max = thisstyle.maxw, minnull = min === null, maxnull = max === null, em = "em";

        if (!!min) {

          min = parseFloat(min) * (min.indexOf(em) > -1 ? eminpx || getEmValue() : 1);

        }

        if (!!max) {

          max = parseFloat(max) * (max.indexOf(em) > -1 ? eminpx || getEmValue() : 1);

        }

        if (!thisstyle.hasquery || (!minnull || !maxnull) && (minnull || currWidth >= min) && (maxnull || currWidth <= max)) {

          if (!styleBlocks[thisstyle.media]) {

            styleBlocks[thisstyle.media] = [];

          }

          styleBlocks[thisstyle.media].push(rules[thisstyle.rules]);

        }

      }

    }

    for (var j in appendedEls) {

      if (appendedEls.hasOwnProperty(j)) {

        if (appendedEls[j] && appendedEls[j].parentNode === head) {

          head.removeChild(appendedEls[j]);

        }

      }

    }

    appendedEls.length = 0;

    for (var k in styleBlocks) {

      if (styleBlocks.hasOwnProperty(k)) {

        var ss = doc.createElement("style"), css = styleBlocks[k].join("\n");

        ss.type = "text/css";

        ss.media = k;

        head.insertBefore(ss, lastLink.nextSibling);

        if (ss.styleSheet) {

          ss.styleSheet.cssText = css;

        } else {

          ss.appendChild(doc.createTextNode(css));

        }

        appendedEls.push(ss);

      }

    }

  }, translate = function(styles, href, media) {

    var qs = styles.replace(respond.regex.comments, "").replace(respond.regex.keyframes, "").match(respond.regex.media), ql = qs && qs.length || 0;

    href = href.substring(0, href.lastIndexOf("/"));

    var repUrls = function(css) {

      return css.replace(respond.regex.urls, "$1" + href + "$2$3");

    }, useMedia = !ql && media;

    if (href.length) {

      href += "/";

    }

    if (useMedia) {

      ql = 1;

    }

    for (var i = 0; i < ql; i++) {

      var fullq, thisq, eachq, eql;

      if (useMedia) {

        fullq = media;

        rules.push(repUrls(styles));

      } else {

        fullq = qs[i].match(respond.regex.findStyles) && RegExp.$1;

        rules.push(RegExp.$2 && repUrls(RegExp.$2));

      }

      eachq = fullq.split(",");

      eql = eachq.length;

      for (var j = 0; j < eql; j++) {

        thisq = eachq[j];

        if (isUnsupportedMediaQuery(thisq)) {

          continue;

        }

        mediastyles.push({

          media: thisq.split("(")[0].match(respond.regex.only) && RegExp.$2 || "all",

          rules: rules.length - 1,

          hasquery: thisq.indexOf("(") > -1,

          minw: thisq.match(respond.regex.minw) && parseFloat(RegExp.$1) + (RegExp.$2 || ""),

          maxw: thisq.match(respond.regex.maxw) && parseFloat(RegExp.$1) + (RegExp.$2 || "")

        });

      }

    }

    applyMedia();

  }, makeRequests = function() {

    if (requestQueue.length) {

      var thisRequest = requestQueue.shift();

      ajax(thisRequest.href, function(styles) {

        translate(styles, thisRequest.href, thisRequest.media);

        parsedSheets[thisRequest.href] = true;

        w.setTimeout(function() {

          makeRequests();

        }, 0);

      });

    }

  }, ripCSS = function() {

    for (var i = 0; i < links.length; i++) {

      var sheet = links[i], href = sheet.href, media = sheet.media, isCSS = sheet.rel && sheet.rel.toLowerCase() === "stylesheet";

      if (!!href && isCSS && !parsedSheets[href]) {

        if (sheet.styleSheet && sheet.styleSheet.rawCssText) {

          translate(sheet.styleSheet.rawCssText, href, media);

          parsedSheets[href] = true;

        } else {

          if (!/^([a-zA-Z:]*\/\/)/.test(href) && !base || href.replace(RegExp.$1, "").split("/")[0] === w.location.host) {

            if (href.substring(0, 2) === "//") {

              href = w.location.protocol + href;

            }

            requestQueue.push({

              href: href,

              media: media

            });

          }

        }

      }

    }

    makeRequests();

  };

  ripCSS();

  respond.update = ripCSS;

  respond.getEmValue = getEmValue;

  function callMedia() {

    applyMedia(true);

  }

  if (w.addEventListener) {

    w.addEventListener("resize", callMedia, false);

  } else if (w.attachEvent) {

    w.attachEvent("onresize", callMedia);

  }

})(this);

直接下载>>respond.zip<<文件