Vue封装一个简单轻量的上传文件组件的示例

methods: {
  addFile, remove, submit, checkIfCanUpload
}

addFile({target: {files}}){//input标签触发onchange事件时，将文件加入待上传列表
 for(let i = 0, l = files.length; i  0 && l > limit){//有数目限制时，取后面limit个文件
  limit = Math.ceil(limit);
//  limit = limit > 10 &＃63; 10 : limit;
  fileList = fileList.slice(l - limit);
 }
 }else{//单选时，只取最后一个文件。注意这里没写成fileList = files;是因为files本身就有多个元素（比如选择文件时一下子框了一堆）时，也只要一个
 fileList = [files[0]];
 }
 this.onChange(fileList);//调用父组件方法，将列表缓存到上一级data中的fileList属性
 },

remove(index){
 let fileList = [...this.fileList];
 if(fileList.length){
 fileList.splice(index, 1);
 this.onChange(fileList);
 }
},

submit(){
 if(this.checkIfCanUpload()){
 if(this.onProgress && typeof XMLHttpRequest !== 'undefined')
  this.xhrSubmit();
 else
  this.fetchSubmit();
 }
},

fetchSubmit(){
 let keys = Object.keys(this.data), values = Object.values(this.data), action = this.action;
 const promises = this.fileList.map(each => {
 each.status = "uploading";
 let data = new FormData();
 data.append(this.name || 'file', each);
 keys.forEach((one, index) => data.append(one, values[index]));
 return fetch(action, {
  method: 'POST',
  headers: {
   "Content-Type" : "application/x-www-form-urlencoded"
  },
  body: data
 }).then(res => res.text()).then(res => JSON.parse(res));//这里res.text()是根据返回值类型使用的，应该视情况而定
 });
 Promise.all(promises).then(resArray => {//多线程同时开始，如果并发数有限制，可以使用同步的方式一个一个传，这里不再赘述。
 let success = 0, failed = 0;
 resArray.forEach((res, index) => {
  if(res.code == 1){
  success++;         //统计上传成功的个数，由索引可以知道哪些成功了
  this.onSuccess(index, res);
  }else if(res.code == 520){   //约定失败的返回值是520
  failed++;         //统计上传失败的个数，由索引可以知道哪些失败了
  this.onFailed(index, res);
  }
 });
 return { success, failed };   //上传结束，将结果传递到下文
 }).then(this.onFinished);      //把上传总结果返回
},

xhrSubmit(){
  const _this = this;
 let optiOns= this.fileList.map((rawFile, index) => ({
 file: rawFile,
 data: _this.data,
    filename: _this.name || "file",
    action: _this.action,
    onProgress(e){
     _this.onProgress(index, e);//闭包，将index存住
    },
    onSuccess(res){
     _this.onSuccess(index, res);
    },
    onError(err){
     _this.onFailed(index, err);
    }
  }));
 let l = this.fileList.length;
 let send = async optiOns=> {
 for(let i = 0; i 

sendRequest(option){

 const _this = this;
  upload(option);

 function getError(action, option, xhr) {
  var msg = void 0;
  if (xhr.response) {
   msg = xhr.status + ' ' + (xhr.response.error || xhr.response);
  } else if (xhr.responseText) {
   msg = xhr.status + ' ' + xhr.responseText;
  } else {
   msg = 'fail to post ' + action + ' ' + xhr.status;
  }

  var err = new Error(msg);
  err.status = xhr.status;
  err.method = 'post';
  err.url = action;
  return err;
 }

 function getBody(xhr) {
  var text = xhr.responseText || xhr.response;
  if (!text) {
   return text;
  }

  try {
   return JSON.parse(text);
  } catch (e) {
   return text;
  }
 }

 function upload(option) {
  if (typeof XMLHttpRequest === 'undefined') {
   return;
  }

  var xhr = new XMLHttpRequest();
  var action = option.action;

  if (xhr.upload) {
   xhr.upload.Onprogress= function progress(e) {
    if (e.total > 0) {
     e.percent = e.loaded / e.total * 100;
    }
    option.onProgress(e);
   };
  }

  var formData = new FormData();

  if (option.data) {
   Object.keys(option.data).map(function (key) {
    formData.append(key, option.data[key]);
   });
  }

  formData.append(option.filename, option.file);

  xhr.Onerror= function error(e) {
   option.onError(e);
  };

  xhr.Onload= function onload() {
   if (xhr.status <200 || xhr.status >= 300) {
    return option.onError(getError(action, option, xhr));
   }

   option.onSuccess(getBody(xhr));
  };

  xhr.open('post', action, true);

  if (option.withCredentials && 'withCredentials' in xhr) {
   xhr.withCredentials = true;
  }

  var headers = option.headers || {};

  for (var item in headers) {
   if (headers.hasOwnProperty(item) && headers[item] !== null) {
    xhr.setRequestHeader(item, headers[item]);
   }
  }
  xhr.send(formData);
  return xhr;
 }
}

checkIfCanUpload(){
 return this.fileList.length &＃63; (this.onBefore && this.onBefore() || !this.onBefore) : false;
},