最近在使用for循环和el-upload上传图片时需要进行数据绑定，要知道存储图片对象的的index，方便进行赋值。
中间想了各类方法， :http-request="httpPicRequest(index，file)"可以解决，但是校验类型比较麻烦
最终选择了before-upload结合bind方式实现:before-upload=" handleBeforePicUpload.bind(null, { type: '.jpg,.png' })"，记录一下方便以后在遇到类似问题能想起来。
<el-upload
:file-list="coverPicList"
:action="action"
list-type="picture-card"
:limit="1"
:data="fileData"
accept=".jpg,.png"
:before-upload="
handleBeforePicUpload.bind(null, { type: '.jpg,.png' ,index:index})
"
:on-preview="handleUploadPicPreview"
:on-remove="handleCoverPicRemove"
:on-error="handleUploadPicError"
:on-exceed="handleExceed"
:multiple="false"
>
<i class="el-icon-plus"></i>
<div slot="file" slot-scope="{ file }">
<img
class="el-upload-list__item-thumbnail"
:src="file.url"
/>
<span class="el-upload-list__item-actions">
<span
class="el-upload-list__item-preview"
@click="handleUploadPicPreview(file)"
>
<i class="el-icon-zoom-in"></i>
</span>
<span
class="el-upload-list__item-delete"
@click="handleCoverPicRemove(file)"
>
<i class="el-icon-delete"></i>
</span>
</span>
</div>
</el-upload>
