我有一个简单的节点.js快速服务器是这样的：
const express = require('express');
const app = express();
const port = process.env.PORT || 5000;
app.listen(port, () => console.log(`Listening on port ${port}`));
app.get('/express_backend', (req, res) => {
res.send({ express: 'YOUR EXPRESS BACKEND IS CONNECTED TO REACT' });
});
并在 package.json 中设置代理，如下所示：
"proxy": "http://localhost:5000/"
使用以下应用程序.js文件
class App extends Component {
constructor(){
super();
this.state = {data: "asdf"};
}
componentDidMount() {
fetch('/express_backend')
.then(res => res.json())
.then(res => this.setState({data: res.express}));
}
我目前正在运行node server.js和npm start。
但是，当我运行它时，我在控制台中收到以下消息
，用于行react-dom.development.js:26607：语法错误：JSON.parse：第 1 行第 1 列 中的意外字符 JSON数据
"/express_backend"的响应内容如下：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<link rel="shortcut icon" href="/favicon.ico" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<meta name="theme-color" content="#000000" />
<meta
name="description"
content="Web site created using create-react-app"
/>
<link rel="apple-touch-icon" href="logo192.png" />
<!--
manifest.json provides metadata used when your web app is installed on a
user's mobile device or desktop. See https://developers.google.com/web/fundamentals/web-app-manifest/
-->
<link rel="manifest" href="/manifest.json" />
<!--
Notice the use of in the tags above.
It will be replaced with the URL of the `public` folder during the build.
Only files inside the `public` folder can be referenced from the HTML.
Unlike "/favicon.ico" or "favicon.ico", "/favicon.ico" will
work correctly both with client-side routing and a non-root public URL.
Learn how to configure a non-root public URL by running `npm run build`.
-->
<title>React App</title>
</head>
<body>
<noscript>You need to enable JavaScript to run this app.</noscript>
<div id="root"></div>
<!--
This HTML file is a template.
If you open it directly in the browser, you will see an empty page.
You can add webfonts, meta tags, or analytics to this file.
The build step will place the bundled scripts into the <body> tag.
To begin the development, run `npm start` or `yarn start`.
To create a production bundle, use `npm run build` or `yarn build`.
-->
<script src="/static/js/bundle.js"></script><script src="/static/js/0.chunk.js"></script><script src="/static/js/main.chunk.js"></script></body>
</html>
我现在也得到了这个，如果它有任何用处：
Source map error: SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data
Resource URL: http://localhost:3000/
Source Map URL: ../sourcemaps/inpage.js.map
您将res.send替换为res.json。
与其依靠res.json()为您打电话JSON.stringify，不如尝试明确地执行此操作：
res.json(JSON.stringify({ express: 'YOUR EXPRESS BACKEND IS CONNECTED TO REACT' }))