ajax--表单带file数据提交报错Uncaught TypeError: Illegal invocation

 1  $("#btn").on("click",function(e){
 2         e.preventDefault();
 3         // 得到提交的参数
 4         var name = $("#name").val();
 5         var gender = $("input[type=‘radio‘]:checked").val(); 
 6         var img = $("#preView").attr("src");
 7         var fm = new FormData();
 8        
 9         fm.append("name",name);
10         fm.append("gender",gender);
11         fm.append("img",img);
12         $.ajax({
13             url:"/add",
14             type:‘POST‘,
15             dataType:‘JSON‘,
16             data:fm,
17             contentType: false, //不设置内容类型  
18             processData: false, //不处理数据  
19             success:function(data){
20                 if(data.status == 1){
21                     alert(data.msg);
22                     window.location= "/";
23                 }else{
24                     alert(data.msg);
25                 }
26             }
27         });
28     });