Element-UI的Upload组件如何实现上传文件的长尾词缓存处理？

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Element-UI的文件上传组件主要功能是重定向文件上传到后端处理，需要action属性作为必填属性。但如果需要读取本地文件并在前端直接处理，则文件无需上传到后端。

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：

<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>

PS： 相关阅读

developer.mozilla.org/zh-CN/docs/Web/API/FileReader

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