Element-UI中上传的文件前端处理

Element-UI对于文件上传组件的功能点着重于文件传递到后台处理，所以要求action为必填属性。但是如果需要读取本地文件并在前端直接处理，文件就没有必要传递到后台，比如在本地打开一个JSON文件，利用JSON文件在前端进行动态展示等等。

下面就展示一下具体做法：

首先定义一个jsonContent, 我们的目标是将本地选取的文件转换为JSON赋值给jsonContent

然后我们的模板文件是利用el-dialog和el-upload两个组件组合：这里停止文件自动上传模式:auto-upload="false"

  <el-button type="primary" @click="dialogVisible = true">Load from File</el-button>
  <el-dialog title="Load JSON document from file" :visible.sync="dialogVisible">
    <el-upload :file-list="uploadFiles" action="alert" :auto-upload="false" multiple :on-change="loadJsonFromFile">
      <el-button size="small" type="primary">Select a file</el-button>
      <div slot="tip">upload only jpg/png files, and less than 500kb</div>
    </el-upload>
    <span slot="footer">
      <el-button type="primary" @click="dialogVisible = false">cancel</el-button>
      <el-button type="primary" @click="loadJsonFromFileConfirmed">confirm</el-button>
    </span>
  </el-dialog>

最后通过html5的filereader对变量uploadFiles中的文件进行读取并赋值给jsonContent

if (this.uploadFiles) {
        for (let i = 0; i < this.uploadFiles.length; i++) {
          let file = this.uploadFiles[i]
          console.log(file.raw)
          if (!file) continue
          let reader = new FileReader()
          reader.onload = async (e) => {
            try {
              let document = JSON.parse(e.target.result)
              console.log(document)
            } catch (err) {
              console.log(`load JSON document from file error: ${err.message}`)
              this.showSnackbar(`Load JSON document from file error: ${err.message}`, 4000)
            }
          }
          reader.readAsText(file.raw)
        }
      }

为方便测试，以下是完整代码：

另外一篇文章是介绍如何将jsonContent变量中的JSON对象保存到本地文件

<template>
  <div>
    <el-button type="primary" @click="dialogVisible = true">Load from File</el-button>
  <el-dialog title="Load JSON document from file" :visible.sync="dialogVisible">
    <el-upload :file-list="uploadFiles" action="alert" :auto-upload="false" multiple :on-change="loadJsonFromFile">
      <el-button size="small" type="primary">Select a file</el-button>
      <div slot="tip">upload only jpg/png files, and less than 500kb</div>
    </el-upload>
    <span slot="footer">
      <el-button type="primary" @click="dialogVisible = false">cancel</el-button>
      <el-button type="primary" @click="loadJsonFromFileConfirmed">confirm</el-button>
    </span>
  </el-dialog>
</div>

</template>

<script>
export default {
  data () {
    return {
      // data for upload files
      uploadFilename: null,
      uploadFiles: [],
      dialogVisible: false
    }
  },
  methods: {
    loadJsonFromFile (file, fileList) {
      this.uploadFilename = file.name
      this.uploadFiles = fileList
    },
    loadJsonFromFileConfirmed () {
      console.log(this.uploadFiles)
      if (this.uploadFiles) {
        for (let i = 0; i < this.uploadFiles.length; i++) {
          let file = this.uploadFiles[i]
          console.log(file.raw)
          if (!file) continue
          let reader = new FileReader()
          reader.onload = async (e) => {
            try {
              let document = JSON.parse(e.target.result)
              console.log(document)
            } catch (err) {
              console.log(`load JSON document from file error: ${err.message}`)
              this.showSnackbar(`Load JSON document from file error: ${err.message}`, 4000)
            }
          }
          reader.readAsText(file.raw)
        }
      }
      this.dialogVisible = false
    }
  }
}
</script>