连接到 API 时出现 REACT、NODE、EXPRESS 错误

Question

我收到错误：

localhost/:1 Failed to load http://localhost:5000/api/hello: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:3000' is therefore not allowed access. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

这是我的异步 POST:

async function submitToServer(data){

  try{
      let response = await fetch('http://localhost:5000/api/hello', {
          method: 'POST',
          headers: {
            'Content-type' :  'application/json',
          },
          body: JSON.stringify(data),
        });
        let responseJson = await response.json();
        return responseJson;
  }   catch (error) {
          console.error(error);
  }
}

这是我的服务器：

const express = require('express');

const app = express();
const port = process.env.PORT || 5000;

app.get('/api/hello', (req, res) => {
  res.send({ express: 'Hello From Express' });
});

app.listen(port, () => console.log(`Listening on port ${port}`));

我应该怎么做才能将此信息发送到 API？
我是否需要创建端点或其他东西？

所以我安装了cors npm。
现在我有这些错误：

POST localhost:5000/api/hello 404 (Not Found)

和

SyntaxError: Unexpected token < in JSON at position 0

我现在可以做什么？

Answer 1

您没有从您的快递服务器返回 JSON。

res.send({ express: 'Hello From Express' });

应该是

res.json({ express: 'Hello From Express' });

此外，您为 GET 定义了路由，但您发送了 POST 请求。所以你的处理程序应该是：

app.post('/api/hello', (req, res) => {
  res.json({ express: 'Hello From Express' });
});

连接到 API 时出现 REACT、NODE、EXPRESS 错误

REACT, NODE, EXPRESS Error when connect to API

api

endpoint

express

reactjs