JS中FileReader實現圖片上傳預覽

<p id="wrapper"> 
 <input id="fileUpload" type="file" multiple /><br />
 <p id="image-holder"> </p>
</p>

$("#fileUpload").on('change', function () {
 
 //獲取上傳文件的數量
 var countFiles = $(this)[0].files.length;
 
 var imgPath = $(this)[0].value;
 var extn = imgPath.substring(imgPath.lastIndexOf('.') + 1).toLowerCase();
 var image_holder = $("#image-holder");
 image_holder.empty();
 if (extn == "gif" || extn == "png" || extn == "jpg" || extn == "jpeg") {
 if (typeof (FileReader) != "undefined") { 
 // 循環所有要上傳的圖片
 for (var i = 0; i < countFiles; i++) {
 
 var reader = new FileReader();
 reader.onload = function (e) {
 $("<img />", {
 "src": e.target.result,
 "class": "thumb-image"
 }).appendTo(image_holder);
 }
 image_holder.show();
 reader.readAsDataURL($(this)[0].files[i]);
 }
 } else {
 alert("你的瀏覽器不支持FileReader！");
 }
 } else {
 alert("請選擇圖像文件。");
 }
});