<input type="file" accept="image/jpg,image/jpeg,image/png,image/gif" id="upload">
<input type="hidden" name="file"> 

 <script type="text/javascript">
function($){
 //上传
 $("#upload").on("change", function () {
 //构造FormData对象并赋值
  var formData = new FormData();
  formData.append("policy", "//controller层传递过来upYun的policy配置");
  formData.append("signature", "//controller层传递过来upyun的signature配置");
  formData.append("file", $("#upload")[0].files[0]);
  $.ajax({
   url : "//处理上传的后端程序地址",
   type : "POST",
   data : formData,
   processData : false,
   contentType : false,
   beforeSend: function () {
    //可以做一些正在上传的效果
   },
   success : function(data) {
    //data，我们这里是异步上传到后端程序所返回的图片地址
   },
   error : function(responseStr) {
    console.log(responseStr);
   }
  });
 });
}($);
</script>