看起来他们改变了create-react-app利用代理的方式。proxy从中删除package.json。然后…

添加此包：

npm i -S http-proxy-middleware

然后创建一个setupProxy.js在src：

src / setupProxy.js

const proxy = require("http-proxy-middleware");

module.exports = app => {
  app.use(proxy("/api/*", { target: "http://localhost:5000/" }));
};

现在，从React组件内部，您可以执行以下操作：

src / App.js

import React, { Component } from "react";
import logo from "./logo.svg";
import "./App.css";

export default class App extends Component {
  state = {
    message: "",
    error: "",
    eee: "",
    text: ""
  };

  componentDidMount = () => this.fetchAPIMessage();

  fetchAPIMessage = async () => {
    try {
      const res = await fetch(`/api/message`);
      const { message } = await res.json();
      this.setState({ message });
    } catch (err) {
      console.error(err);
    }
  };

  render = () => (
    <div className="App">
      <header className="App-header">
        <img src={logo} className="App-logo" alt="logo" />
        <p>WELCOME CREATE REACT APP!</p>
        <div className="App-link">{this.state.message}</div>
      </header>
    </div>
  );
}

index.js （我添加npm i -D morgan了一个方便的日志记录框架，当请求命中API时，它将在控制台中显示它）。

const path = require("path");
const express = require("express");
const app = express();
const morgan = require("morgan");

app.use(morgan("tiny")); // logging framework

// Serve our api message
app.get("/api/message", async (req, res, next) => {
  try {
    res.status(201).json({ message: "HELLOOOOO FROM EXPRESS" });
  } catch (err) {
    next(err);
  }
});

if (process.env.NODE_ENV === "production") {
  // Express will serve up production assets
  app.use(express.static("build"));

  // Express will serve up the front-end index.html file if it doesn't recognize the route
  app.get("*", (req, res) =>
    res.sendFile(path.resolve("build", "index.html"))
  );
}

// Choose the port and start the server
const PORT = process.env.PORT || 5000;
app.listen(PORT, () => console.log(`Mixing it up on port ${PORT}`));

package.json （用于node提供生产资产-请参见“开始”脚本）

{
  "name": "proxytest",
  "version": "0.1.0",
  "private": true,
  "homepage": "https://proxytest2.herokuapp.com/",
  "dependencies": {
    "concurrently": "^4.0.1",
    "express": "^4.16.4",
    "http-proxy-middleware": "^0.19.0",
    "react": "^16.5.2",
    "react-dom": "^16.5.2",
    "react-scripts": "2.0.5",
    "serve": "^10.0.2"
  },
  "scripts": {
    "start": "NODE_ENV=production node index.js",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "client": "react-scripts start",
    "server": "nodemon server",
    "eject": "react-scripts eject",
    "dev": "concurrently --kill-others-on-fail \"npm run server\" \"npm run client\"",
    "heroku-postbuild": "npm run build"
  },
  "eslintConfig": {
    "extends": "react-app"
  },
  "browserslist": [
    ">0.2%",
    "not dead",
    "not ie <= 11",
    "not op_mini all"
  ]
}

在以下位置运行时，您将在控制台中看到的内容production：

m6d@m6d-pc:~/Desktop/proxytest-master$ npm start

> [email protected] start /home/m6d/Desktop/proxytest-master
> NODE_ENV=production node index.js

Mixing it up on port 5000
GET / 200 2057 - 6.339 ms
GET /static/css/main.068b9d02.chunk.css 304 - - 1.790 ms
GET /static/js/1.9a879072.chunk.js 304 - - 0.576 ms
GET /static/js/main.e3ba6603.chunk.js 304 - - 0.605 ms
GET /api/message 201 36 - 4.299 ms
GET /static/media/logo.5d5d9eef.svg 304 - - 0.358 ms

其他说明：

• 确保将您的客户端src与API分开（例如，将前端React应用程序中的所有内容放入client具有自己依赖项的文件夹中）。
• 从您的API中删除所有React依赖项 package.json