实例讲解javascript实现异步图片上传方法

<form id="uploadForm" action="http://storage.test.com/file/upload" method="post" enctype="multipart/form-data">
 <input type="hidden" name="key" id="key" value="VTZ18HM#D_L3WX" />
 <input type="file" name="uploadFiles" value="" id="fileImage" multiple='multiple' />
 <div class="upload_submit">
 <button type="button" id="fileSubmit" class="upload_btn">保存</button>
 </div>
</form>

var Fileupload = {
 fileInput: $("#fileImage").get(0),
 dragDrop: $("#fileDragArea").get(0),
 upButton: $("#fileSubmit").get(0),
 url: $("#uploadForm").attr("action"),
 })(),
 //文件上传
 funUploadFile: function() {
 var self = this;
 for (var i = 0, file; file = this.fileFilter[i]; i++) {
 (function(file) {
 var xhr = new XMLHttpRequest();
 if (xhr.upload) {
 // 上传中
 xhr.upload.addEventListener("progress", function(e) {
 self.onProgress(file, e.loaded, e.total);
 }, false);
 // 文件上传成功或是失败
 xhr.onreadystatechange = function(e) {

 if (xhr.readyState == 4) {
 if (xhr.status == 200) {
 self.onSuccess(JSON.parse(xhr.responseText));
 self.funDeleteFile(file);
 if (!self.fileFilter.length) {
 //全部完毕
 self.onComplete();
 }
 } else {
 self.onFailure(file, xhr.responseText);
 }
 }
 };
 //准备FormData对象
 var myForm = document.getElementById('uploadForm');
 //将文件放入FormData对象中
 formData = new FormData(myForm);

 // 开始上传
 xhr.open("POST", self.url, true);
 xhr.send(formData);
 }
 })(file);
 }
 },
 init: function() {
 var self = this；
 //上传按钮提交
 if (this.upButton) {
 console.log('提示： 当前存储服务器地址', this.url)
 this.upButton.addEventListener("click", function(e) {
 self.funUploadFile(e);
 }, false);
 }
 self.bindEvent();
 }
 };
 Fileupload = $.extend(Fileupload);
 Fileupload.init();

<input type="file" id="file">

//准备FormData对象
var formData = new FormData(),
 uploadFile = document.getElementById('file');
 
//将文件放入FormData对象中 
formData.append('file', uploadFile.files[0]);

//创建xhr对象
var xhr = new XMLHttpRequest();

//监听文件上传进度
xhr.upload.onprogress = function(evt){
 //lengthComputabel: 文件长度是否可计算
 if(evt.lengthComputable){
 //evt.loaded: 已下载的字节数
 //evt.total: 文件总字节数
 var percent = Math.round(evt.loaded*100/evt.total);
 console.log(percent);
 }
}

//监听文件传输开始 
xhr.onloadstart = function(evt）{
 xhr.abort() //终止上传
}

//监听ajax成功完成事件
xhr.onload = function(evt){
 ...
}

//监听ajax错误事件 
xhr.onerror = function(evt){
 ...
}

//监听ajax被中止事件
xhr.onabort = function(evt){
 ...
}

//监听传输结束事件: 不管成功或者失败都会触发
xhr.onloaded = function(evt){
 ...
}
 
//*发起ajax请求数据
xhr.open('POST', '/url', true);
xhr.send(formData);