How to allow CORS in node.js?

I have a React app (localhost:3000) and a Node app (localhost:3001) to run a simple system. The problem is I’m getting the error Access to XMLHttpRequest at 'localhost:3001/app' from origin 'http://localhost:3000' has been blocked by CORS policy: Cross origin requests are only supported for protocol schemes: http, data, chrome, chrome-extension, chrome-untrusted, https.

I have tried with app.use(cors()) and also with cors options as below. Still I’m getting the above error.

Node app.js

const express = require('express');
const app = express();
const cors = require('cors');

const corsOptions = {
    origin: 'http://localhost:3000/',
    credentials: true,
    optionSuccessStatus: 200
}

app.use(cors(corsOptions));

app.use(function (req, res, next) {
    res.header('Access-Control-Allow-Origin', "http://localhost:3000");
    res.header('Access-Control-Allow-Headers', true);
    res.header('Access-Control-Allow-Credentials', true);
    res.header('Access-Control-Allow-Methods', 'GET, POST, OPTIONS, PUT, PATCH, DELETE');
    next();
});

app.use(express.json());

app.get('/app', (req, res) => {
    res.send({result: "hello"});
});

module.exports = app;

React app.js

import React, { Component } from "react";
import axios from 'axios';

class App extends Component {

componentDidMount(){ this.runInstance(); }

runInstance = () => {
        axios.get(`localhost:3001/app`)
        .then(res => {
            console.log("res", res);
        })
        .catch(err => {
            console.log("AXIOS ERROR:", err);
        })
    }

render() { return(<div></div>) }
}
export default App;

How can I solve this?

>Solution :

Since you use nodejs

installing cors

npm install cors

After that

var express = require('express')
var cors = require('cors')
var app = express()

app.use(cors())

app.get('/products/:id', function (req, res, next) {
  res.json({msg: 'This is CORS-enabled for all origins!'})
})

app.listen(80, function () {
  console.log('CORS-enabled web server listening on port 80')
})

Then after applying "cors" middleware. You need to insert "http://" before "localhost: in your react app".

Example

axios.get(`http://localhost:3001/api/app`)
        .then(res => {
            console.log("res", res);
        })
        .catch(err => {
            console.log("AXIOS ERROR:", err);
        })