您可以使用FileReader

var FormBox = React.createCl({
          getInitialState: function () {
            return {
              file: '',
              imagePreviewUrl: ''
            }
          },
          pressButton: function () {
            e.preventDefault();
          // TODO: do something with -> this.state.file
          console.log('handle uploading-', this.state.file);
          },
          getPhoto: function (e) {
            e.preventDefault();
            let reader = new FileReader();
            let file = e.target.files[0];
            reader.onloadend = () => {
              this.setState({
                file: file,
                imagePreviewUrl: reader.result
              });
            }
            reader.readAsDataURL(file);
            
          },
          render: function () {
            let {imagePreviewUrl} = this.state;
            let imagePreview = null;
            if (imagePreviewUrl) {
              imagePreview = (<img src={imagePreviewUrl} />);
            } else {
              imagePreview = (<div clName="previewText">Please select an Image for Preview</div>);
            }
            return (
              <div>
              <form action='.' enctype="multipart/form-data">
                <input type='file'  onChange={this.getPhoto}/>
                <on onClick={this.pressButton}> Get it </on>
              </form>
              <div clName="imgPreview">
                {imagePreview}
              </div>
              </div>
            )
          }
        })
        
        ReactDOM.render(<FormBox />, document.getElementById('root'))

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/0.14.8/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/0.14.8/react-dom.min.js"></script>
<div id="root"></div>

如果您计划使用 node 和 express 上传文件，那么您必须创建服务器和客户端。服务器有 api，客户端将使用 axios 上传文件。

服务器部件

首先，我们想放入四个包，分别是 express 、 explicit-fileupload 、 cors 和 nodemon。运行下面的命令来安装应用程序。

npm i express express-fileupload cors nodemon

现在，在您喜欢的代码编辑器中打开 fileupload 文件夹，并创建一个称为 server.js 的全新文档。

// server.js
const express = require('express');
const fileUpload = require('express-fileupload');
const cors = require('cors')
const app = express();
// middle ware
app.use(express.static('public')); //to access the files in public folder
app.use(cors()); // it enables all cors requests
app.use(fileUpload());
// file upload api
app.post('/upload', (req, res) => {
    if (!req.files) {
        return res.status(500).send({ msg: "file is not found" })
    }
        // accessing the file
    const myFile = req.files.file;
    //  mv() method places the file inside public directory
    myFile.mv(`${__dirname}/public/${myFile.name}`, function (err) {
        if (err) {
            console.log(err)
            return res.status(500).send({ msg: "Error occured" });
        }
        // returing the response with file path and name
        return res.send({name: myFile.name, path: `/${myFile.name}`});
    });
})
app.listen(4500, () => {
    console.log('server is running at port 4500');
})

使用node server.js启动服务器运行。

在您喜欢的代码编辑器上打开 react app 文件夹，并在 src 文件夹中创建一个名为 fileupload.js 的全新报告。现在上传以下代码。

// fileupload.js
import React, { useRef, useState } from 'react';
import axios from 'axios';
function FileUpload() {
    const [file, setFile] = useState(''); // storing the uploaded file    
    // storing the recived file from backend
    const [data, getFile] = useState({ name: "", path: "" });    
    const [progress, setProgess] = useState(0); // progess bar
    const el = useRef(); // accesing input element
    const handleChange = (e) => {
        setProgess(0)
        const file = e.target.files[0]; // accesing file
        console.log(file);
        setFile(file); // storing file
    }
    const uploadFile = () => {
        const formData = new FormData();        
        formData.append('file', file); // appending file
        axios.post('http://localhost:4500/upload', formData, {
            onUploadProgress: (ProgressEvent) => {
                let progress = Math.round(
                ProgressEvent.loaded / ProgressEvent.total * 100) + '%';
                setProgess(progress);
            }
        }).then(res => {
            console.log(res);
            getFile({ name: res.data.name,
                     path: 'http://localhost:4500' + res.data.path
                   })
        }).catch(err => console.log(err))}
    return (
        <div>
            <div clName="file-upload">
                <input type="file" ref={el} onChange={handleChange} />                
                <div clName="progessBar" style={{ width: progress }}>
                   {progress}
                </div>
                <on onClick={uploadFile} clName="upon">                   
                    Upload
                </on>
            <hr />
            {/* displaying received video*/}
            {data.path && <video src={data.path} autoPlay controls />}
            </div>
        </div>
    );
}
export default FileUpload;

现在，在 App.js 文件中导入 FileUpload 组件。

// App.js
import React from 'react';
import FileUpload from './fileupload';
import './App.css';
function App() {
  return (
    <div clName="App">
      <FileUpload />
    </div >
  );
}
export default App;

通过运行npm start启动 react 应用程序。

更多信息：React File Upload Demo

import axios from 'axios';
var FormBox = React.createCl({
  getInitialState: function () {
    return {
      photo: [],
      name : '',
      documents:[]
    }
  },
  pressButton: function () {
    var component = this
    var data = new FormData();
    data.append("photo", component.state.photo, component.state.name);
    var request = axios.post('http://localhost:3000/document', data)
        request.then(function(response){
    // you need to send data from server in response
          if(response.status == 200){
             console.log('saved in db')
             component.state.documents.push(response.data.documents)
             // pushed document data in documents array
           }
        })
  },
  getPhoto: function () {
    var uploadfile = document.getElementById(upload_doc).files[0]
    this.setState({
      photo: uploadfile, name : uploadfile.name
    })
  },
  render: function () {
    var documents = this.state.documents.map((doc)=>{
       return <div>
                <a href={doc.url}>{doc.name}</a>
                <img src={doc.photo} />
              </div>
    })
   // you can show your documents uploaded this way using map function
    return (
      <form action='.' enctype="multipart/form-data">
        <input type='file' id='upload_doc'  onChange={this.getPhoto}/>
        <on onClick={this.pressButton}> Get it </on>
        <span>{documents}</span>
        // this way you can see uploaded documents
      </form>
    )
  }
})
ReactDOM.render(<FormBox />, document.getElementById('root'))

一种更简单的方法，通过使用 axios 节点模块axios-fileupload

npm install --save axios-fileupload
const axiosFileupload = require('axios-fileupload'); 
axiosFileupload(url,file);