用一句代码即可搞定：

复制代码 代码如下:

document.execCommand("BackgroundImageCache", false, true);

当然为了其它浏览器上能正常通过，需要做下判断后调用，才更安全：

复制代码 代码如下:

if(Browser.isIE6){

try{

document.execCommand("BackgroundImageCache", false, true);

}

catch(e1){}

}

平台检测代码可以这样写，摘自Ext源码：

复制代码 代码如下:

var Browser = {};

try{

(function(){

var idSeed = 0,

ua = navigator.userAgent.toLowerCase(),

check = function(r){

return r.test(ua);

},

DOC = document,

isStrict = DOC.compatMode == "CSS1Compat",

isOpera = check(/opera/),

isChrome = check(/bchromeb/),

isWebKit = check(/webkit/),

isSafari = !isChrome && check(/safari/),

isSafari2 = isSafari && check(/applewebkit/4/), // unique to Safari 2

isSafari3 = isSafari && check(/version/3/),

isSafari4 = isSafari && check(/version/4/),

isIE = !isOpera && check(/msie/),

isIE7 = isIE && check(/msie 7/),

isIE8 = isIE && check(/msie 8/),

isIE6 = isIE && !isIE7 && !isIE8,

isGecko = !isWebKit && check(/gecko/),

isGecko2 = isGecko && check(/rv:1.8/),

isGecko3 = isGecko && check(/rv:1.9/),

isBorderBox = isIE && !isStrict,

isWindows = check(/windows|win32/),

isMac = check(/macintosh|mac os x/),

isAir = check(/adobeair/),

isLinux = check(/linux/),

isIpad = check(/ipad/),

isSecure = /^https/i.test(window.location.protocol);

extend(Browser,{

isOpera:isOpera,

isIE:isIE,

isIE6:isIE6,

isFirefox:isGecko,

isSafari:isSafari,

isChrome:isChrome,

isIpad:isIpad

});

})();

}catch(e){}

//上面extend方法也很easy

复制代码 代码如下:

function extend(obj1,obj2){

for(var o in obj2){

obj1[o] = obj2[o];

}

return obj1;

}