vue2.0 使用element-ui里的upload组件实现图片预览效果方法

<el-upload class="upload-demo" action="" :auto-upload='false' :on-change='changeUpload'>
 <el-button size="small" type="primary">点击上传</el-button>
 <div slot="tip" class="el-upload__tip">只能上传jpg/png文件，且不超过500kb</div>
</el-upload> 

changeUpload: function(file, fileList) {
 this.fileList = fileList;
 this.$nextTick(
  () => {
  let upload_list_li = document.getElementsByClassName('el-upload-list')[0].children;
  for (let i = 0; i < upload_list_li.length; i++) {
  let li_a = upload_list_li[i];
  let imgElement = document.createElement("img");
  imgElement.setAttribute('src', fileList[i].url);
  imgElement.setAttribute('style', "max-width:50%;padding-left:25%");
  if (li_a.lastElementChild.nodeName !== 'IMG') { 
  li_a.appendChild(imgElement);
  } 
  }
  });
 }