fileReader 上传图片

 function getImgSrc(target, callback) {
     if (window.FileReader) {
         var oPreviewImg = null, oFReader = new window.FileReader();
         oFReader.onload = function (oFREvent) {
             oPreviewImg = new Image();
             var type = target.files[0].type.split("/")[1];
             var src = oFREvent.target.result;
             oPreviewImg.src = src;

             if (typeof callback == "function") {
                 callback(oPreviewImg, target, type, src);
             }

             return oPreviewImg.src;
         };

         return (function () {
             var aFiles = target.files;
             if (aFiles.length === 0) {
                 return;
             }
             if (!IsImgType(aFiles[0].type)) {
                 alert("You must select a valid image file!");
                 return;
             }

             if (aFiles[0].size > 1024 * 1024) {
                 target.value = "";
                 alert('Please upload image file size less than 1M.');
                 return;
             }

             oFReader.readAsDataURL(aFiles[0]);
         })();
     }
     if (navigator.appName === "Microsoft Internet Explorer") {
         return (function () {
             document.getElementById("imagePreview").filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = target.value;
         })();
     }
 }