<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>

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)
    }
   }

<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>