javascript结合fileReader 实现上传图片

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;
        })();
    }
}