js本地图片上传预览

IE6： 

//img: image object
//file: file inputbox object
img.src = file.value;

IE7-8： 

var src = '';
file.select();
try {
    src = document.selection.createRange().text;
} finally {
    document.selection.empty();
}
src = src.replace(/[)'"%]/g, function(s){ return escape(escape(s)); });
img.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod='scale',src=\"" + src + "\")";

Firefox 6以下： 

img.src = file.files[0].getAsDataURL();

Firefox 3.6 (1.9.2)+，Chrome 7+，IE10+，Opera 11.1+，Safari Nightly build： 

var oFile = file.files[0];
var oFReader = new FileReader();
oFReader.onload = function (oFREvent) {
    img.src = oFREvent.target.result;
};
oFReader.readAsDataURL(oFile);

IE9：不能用IE8的方法，也不支持FileReader，http://html5labs.interoperabilitybridges.com/prototypes/fileapi/fileapi/info 里的FileAPI也不能用，需要进一步调查。 

参考文档： 
https://developer.mozilla.org/en/DOM/FileReader