"POST http://localhost:5000 net err failed" - node.js

Question

I'm trying to send a post request to a node server using axios, here's what I've done in react-js.
axios.post('http://localhost:5000', {
firstName: 'Finn',
lastName: 'Williams'
})
.then((response) => {
console.log(response);
}, (error) => {
console.log(error);
});
And here's what I've done in the server.
const express = require('express')
const app = express()
const port = 5000;
app.get('/', (req, res) => {
res.send('Hello World!')
})
app.listen(port, () => {
console.log(`Example app listening at http://localhost:${port}`)
})
Every time I send the request, I get the following message in the console Access to XMLHttpRequest at 'http://localhost:5000/' from origin 'http://localhost:3000' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.
What should I do to fix that?

Answer 1

Install CORS npm package to configure your express HTTP server cors.
npm install cors
Then import CORS package in your express application file like that:
const express = require('express')
const cors = require('cors')
app.use(cors())
const app = express()
const port = 5000;
app.get('/', (req, res) => {
res.send('Hello World!')
})
app.listen(port, () => {
console.log(`Example app listening at http://localhost:${port}`)
})
Then in your request code, you should to request with GET method. You are using axios.post() which does POST request. And that will response you with 404 because you don't have app.post('/') route handler in your application. So the code should look like this:
const express = require('express')
const cors = require('cors')
app.use(cors())
const app = express()
const port = 5000;
app.get('/', (req, res) => {
res.send('Hello World!')
})
app.post('/', (req, res) => {
res.send(Hello ${req.body.firstName} ${req.body.lastName}!`)`;
})
app.listen(port, () => {
console.log(`Example app listening at http://localhost:${port}`)
})

Answer 2

You can install the cors
npm install cors --save
after that you can add this code on server file
var cors = require('cors')
app.use(cors()) // Use this after the variable declaration

Answer 3

You're not sending CORS headers on your responses, so the requests are denied. This can be easily solved by:
Run npm i cors
Change your code to
const express = require('express')
const cors = require('cors');
const app = express()
const port = 5000;
app.use(cors());
// all the other stuff

Answer 4

This error basically occurs because of a security mechanism that browsers implement called the same-origin policy. It prevents any cross-domain communication which may lead to cyber attacks like cross-site request forgery.
While we develop backend APIs for our frontend apps, we have to enable Cross-Origin Resource Sharing (CORS) in our backend server. To do that there are several libraries, the most common one is Cors package. Install it and use it in your server app as follows-
const express = require('express');
const app = express();
const port = 5000;
app.use(cors());
app.get('/', (req, res) => {
res.send('Hello World!')
})