本文实例讲述了jquery+ajax实现上传图片并显示上传进度功能。分享给大家供大家参考，具体如下：
jquery上传文件用的formdata，上传进度条需要添加xhr的onprogress
html代码如下：
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=no">
<title>Ding Jianlong Html</title>
<link href="https://cdnjs.cloudflare.com/ajax/libs/layer/2.3/skin/layer.css" rel="external nofollow" rel="stylesheet">
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/layer/2.3/layer.js"></script>
</head>
<body>
<!-- 外层div 进度条的整体视觉和位置设置 -->
<div style="width:300px;height: 20px;border: 1px solid #CCC;">
<!-- 内层div 逐渐递增的进度条 -->
<div id="jdt" style="height: 20px;"></div>
</div>
<p>总大小<span id="total"></span>；已上传<span id="loaded"></span>；</p><br>
<form id="mainForm">
选择文件：<input type="file" name="file">
<input type="button" value="上传" onclick="upload()">
</form>
<script>
var uploading = false;
function upload(){
//首先封装一个方法 传入一个监听函数 返回一个绑定了监听函数的XMLHttpRequest对象
var xhrOnProgress=function(fun) {
xhrOnProgress.onprogress = fun; //绑定监听
//使用闭包实现监听绑
return function() {
//通过$.ajaxSettings.xhr();获得XMLHttpRequest对象
var xhr = $.ajaxSettings.xhr();
//判断监听函数是否为函数
if (typeof xhrOnProgress.onprogress !== 'function')
return xhr;
//如果有监听函数并且xhr对象支持绑定时就把监听函数绑定上去
if (xhrOnProgress.onprogress && xhr.upload) {
xhr.upload.onprogress = xhrOnProgress.onprogress;
}
return xhr;
}
}
var data = new FormData($('#mainForm')[0]); //要加【0】
console.log(data);
if(uploading){
layer.alert("文件正在上传中，请稍候");
return false;
}
$.ajax({
type: 'POST',
url: 'upload_file.php', //当前路径
data: data,
dataType: 'json',
processData: false, //序列化，no
contentType: false, //不设置内容类型
beforeSend: function(){
uploading = true;
},
//进度条要调用原生xhr
