let files = this.filePicker.files;
if(!files.length) {
  return;
}

let arr = [];
for(let i = 0, len = files.length; i < len; i++) {
  let item = files[i];
  // 每个文件初始进度为0
  item.progress = '0';

  arr.push(obj);
}

this.fileArr = arr;

// 用数组模拟 files, 用对象模拟 file 对象
let files = [];
for(let i = 0, len = 5; i < len; i++) {
  let obj = {name: 'name_' + 1};

  files.push(obj);
}

let arr = [];
for(let i = 0, len = files.length; i < len; i++) {
  files[i].progress = '0';
  arr.push(files[i]);
}

let files = this.filePicker.files;
if(!files.length) {
  return;
}


let arr = [];
for(let i = 0, len = files.length; i < len; i++) {
  let item = files[i];
  let obj = {};

  obj.name = item.name;
  obj.size = item.size;

  obj.progress = '0';

  arr.push(obj);
}

console.log('files type', Object.prototype.toString.call(files));
// files type [object FileList]
console.log('arr  type', Object.prototype.toString.call(arr));
// arr  type [object Array]

console.log('item type', Object.prototype.toString.call (files[0]));
// item type [object File]
console.log('obj type', Object.prototype.toString.call (obj));
// obj type [object Object]

<div id="app">
  <input type="text" id='a'>
  <span id='b'></span>

  <input type="file" id='file'>
  <button type="button" id='button'>点击更改file属性</button>
</div>

<script>
  // 普通对象设置 setter
  var obj = {};
  Object.defineProperty(obj, 'hello', {
    set: function(newVal) {
      document.getElementById('a').value = newVal;
      document.getElementById('b').innerHTML = newVal;
    }
  });

  document.addEventListener('keyup', function(e){
    obj.hello = e.target.value;
  });

  // File 对象设置 setter
  var fileInput = document.getElementById('file');
  var file;
  fileInput.addEventListener('change', function(e){
    file = fileInput.files[0];

    Object.defineProperty(file, 'progress', {
      set: function(newVal) {
        // document.getElementById('a').value = newVal;
        document.getElementById('b').innerHTML = newVal;
      }
    });
  });

  document.getElementById('button').addEventListener('click', function(){
    file.progress = 'hello file';
  });

</script>