<form action="url" enctype="multipart/form-data" id="myform" method="post">    <input accept="image/*" id="addfile" type="file" /></form> 

$("#addfile").on('change', function () {  var f = $(this).get(0).files[0];  var form = document.getElementById('myform');  var formData = new FormData(form);  formData.append('Filedata', f);  var xhr = new XMLHttpRequest();  xhr.addEventListener("load", uploadComplete, false);  xhr.addEventListener("error", uploadFailed, false);  xhr.open('POST', form.action);  xhr.send(formData);});function uploadComplete(evt){  var data=evt.target.responseText}function uploadFailed(){  alert("上傳失敗！請重試！"); }