通过Ajax方式上传文件(input file)，使用FormData进行Ajax请求

<div  >
                        <input type="file" name="FileUpload" id="FileUpload">
                        <a class="layui-btn layui-btn-mini" id="btn_uploadimg">上传图片</a>
                    </div>

<script type="text/jscript">
 
       $(function () {
           $("#btn_uploadimg").click(function () {
               var fileObj = document.getElementById("FileUpload").files[0]; // js 获取文件对象
               if (typeof (fileObj) == "undefined" || fileObj.size <= 0) {
                   alert("请选择图片");
                   return;
               }
               var formFile = new FormData();
               formFile.append("action", "UploadVMKImagePath");  
               formFile.append("file", fileObj); //加入文件对象
 
               //第一种  XMLHttpRequest 对象
               //var xhr = new XMLHttpRequest();
               //xhr.open("post", "/Admin/Ajax/VMKHandler.ashx", true);
               //xhr.onload = function () {
               //    alert("上传完成!");
               //};
               //xhr.send(formFile);
 
               //第二种 ajax 提交
 
               var data = formFile;
               $.ajax({
                   url: "/Admin/Ajax/VMKHandler.ashx",
                   data: data,
                   type: "Post",
                   dataType: "json",
                   cache: false,//上传文件无需缓存
                   processData: false,//用于对data参数进行序列化处理 这里必须false
                   contentType: false, //必须
                   success: function (result) {
                       alert("上传完成!");
                   },
               })
           })
       })
 
   </script>

　　补充 IE8 不支持.files 写法