│  index.js
└─ src
    ajax.js              [默認上傳請求工具]
    index.vue            [管理FileList數(shù)據(jù)，對外暴露操作文件列表的方法]
    upload-dragger.vue   [拖拽：對文件獲取的邏輯]
    upload-list.vue      [文件列表：純UI組件根據(jù)不同listType展示不同的樣式]
    upload.vue           [對單個文件上傳處理的過程]，會涉及index.vue文件邏輯操作]

methods: {
    handleClick() {
      if (!this.disabled) {
        // 處理選中文件之后，后續(xù)繼續(xù)選中重復(fù)文件無法觸發(fā)change問題
        this.$refs.input.value = null;
        this.$refs.input.click();
      }
    },
    handleKeydown(e) {
      if (e.target !== e.currentTarget) return;
      if (e.keyCode === 13 || e.keyCode === 32) {
        this.handleClick();
      }
    }
},
 render(h) {
    // ...
    const data = {
      on: {
        click: handleClick,
        keydown: handleKeydown
      }
    };
    return (
      <div {...data} tabindex="0" >
        // ...
        <input class="el-upload__input" type="file" ref="input" name={name} on-change={handleChange} multiple={multiple} accept={accept}></input>
      </div>
    );
  }

// ??? upload.vue uploadFiles
if (this.limit && this.fileList.length + files.length > this.limit) {
    this.onExceed && this.onExceed(files, this.fileList);
    return;
}

// ??? upload.vue uploadFiles
let postFiles = Array.prototype.slice.call(files);
if (!this.multiple) { postFiles = postFiles.slice(0, 1); }
if (postFiles.length === 0) { return; }

// upload.vue (onStart) ---> index.vue (handleStart)
handleStart(rawFile) {
  rawFile.uid = Date.now() + this.tempIndex++;
  let file = {
    status: 'ready',
    name: rawFile.name,
    size: rawFile.size,
    percentage: 0,
    uid: rawFile.uid,
    raw: rawFile
  };
  if (this.listType === 'picture-card' || this.listType === 'picture') {
    try {
      file.url = URL.createObjectURL(rawFile);
    } catch (err) {
      console.error('[Element Error][Upload]', err);
      return;
    }
  }
  this.uploadFiles.push(file);
  this.onChange(file, this.uploadFiles);
}

// index.vue
submit() {
  this.uploadFiles
    .filter(file => file.status === 'ready')
    .forEach(file => {
      this.$refs['upload-inner'].upload(file.raw);
    });
}

// ??? upload.vue upload
if (!this.beforeUpload) {
    return this.post(rawFile);
}

// ??? upload.vue upload
const before = this.beforeUpload(rawFile);
// Promise
if (before && before.then) {
    before.then(processedFile => {
      const fileType = Object.prototype.toString.call(processedFile);
      if (fileType === '[object File]' || fileType === '[object Blob]') {
        if (fileType === '[object Blob]') {
          processedFile = new File([processedFile], rawFile.name, {
            type: rawFile.type
          });
        }
        // 將原始值復(fù)制到新構(gòu)建的File對象中
        for (const p in rawFile) {
          if (rawFile.hasOwnProperty(p)) {
            processedFile[p] = rawFile[p];
          }
        }
        this.post(processedFile);
      } else {
        this.post(rawFile);
      }
    }, () => {
      // 停止上傳并且從文件列表中刪除
      this.onRemove(null, rawFile);
    });
}
// 非false正常上傳
else if (before !== false) {
    this.post(rawFile);
} else {
// 停止上傳并且從文件列表中刪除
    this.onRemove(null, rawFile);
}

 // index.vue
 handleRemove(file, raw) {
     if (raw) {
       // 獲取當(dāng)前的FileItem對象
       file = this.getFile(raw);
     }
     let doRemove = () => {
       // 中斷正在上傳的文件
       this.abort(file);
       // 移除當(dāng)前FileItem
       let fileList = this.uploadFiles;
       fileList.splice(fileList.indexOf(file), 1);
       // 觸發(fā)回調(diào)
       this.onRemove(file, fileList);
     };
     // 外部沒有傳入beforeRemove直接操作刪除
     if (!this.beforeRemove) {
       doRemove();
     } else if (typeof this.beforeRemove === 'function') {
       const before = this.beforeRemove(file, this.uploadFiles);
       // 和 beforeUpload類似邏輯
       if (before && before.then) {
         before.then(() => {
           doRemove();
         }, noop);
       } else if (before !== false) {
         doRemove();
       }
     }
   }

// ??? upload.vue post
// upload.vue post方法
const { uid } = rawFile;
const options = {
    headers: this.headers,
    withCredentials: this.withCredentials,
    file: rawFile,
    data: this.data,
    filename: this.name,
    action: this.action,
    onProgress: e => {
      this.onProgress(e, rawFile);
    },
    onSuccess: res => {
      this.onSuccess(res, rawFile);
      delete this.reqs[uid];
    },
    onError: err => {
      this.onError(err, rawFile);
      delete this.reqs[uid];
    }
};
const req = this.httpRequest(options);

this.reqs[uid] = req;
if (req && req.then) {
    // 在最后觸發(fā)成功之后，再次調(diào)用回調(diào)
    req.then(options.onSuccess, options.onError);
}

// index.vue
handleProgress(ev, rawFile) {
  const file = this.getFile(rawFile);
  this.onProgress(ev, file, this.uploadFiles);
  file.status = 'uploading';
  file.percentage = ev.percent || 0;
}

 handleSuccess(res, rawFile) {
  const file = this.getFile(rawFile);
  if (file) {
    file.status = 'success';
    file.response = res;
    this.onSuccess(res, file, this.uploadFiles);
    this.onChange(file, this.uploadFiles);
  }
}

handleError(err, rawFile) {
  const file = this.getFile(rawFile);
  const fileList = this.uploadFiles;
  file.status = 'fail';
  fileList.splice(fileList.indexOf(file), 1);
  this.onError(err, file, this.uploadFiles);
  this.onChange(file, this.uploadFiles);
}

// index.vue
// 對外暴露的方法
abort(file) {
      this.$refs['upload-inner'].abort(file);
},
// upload.vue
abort(file) {
  const { reqs } = this;
  // 傳了指定文件
  if (file) {
    // 這里支持傳入是一個uid
    let uid = file;
    if (file.uid) uid = file.uid;
    if (reqs[uid]) {
      // 將指定的請求進行中斷
      reqs[uid].abort();
    }
  } else {
  // 不傳參數(shù)則將正在上傳的全部文件進行中斷
    Object.keys(reqs).forEach((uid) => {
      if (reqs[uid]) reqs[uid].abort();
      delete reqs[uid];
    });
  }
}