Heroku environment variables are not visible for the react app - node.js

Question

I have a Front End application which is mainly based on React, and I have created a node server to serve the application. Build and everything are successful, and the the index.html is also served, but it doesn't read the environment variables that I set through heroku application settings (even from CLI).
Package.json scripts
"scripts": {
"start": "node server",
"start-dev": "react-scripts start",
"start-windows": "set PORT=3001 && react-scripts start",
"build": "react-scripts build",
"postinstall": "npm run build",
"test": "jest src/**/*.test.js",
"eject": "react-scripts eject"
}
node server,
const express = require ('express')
const app = express();
const http = require('http').Server(app);
const path = require( 'path')
let port = process.env.PORT || 3000;
app.use(express.static(path.join(__dirname, 'build')));
app.get('/', (req, res) => {
res.sendFile(path.join(__dirname, 'build') + '/index.html');
});
app.listen(port, () => {
console.log(`App running on port ${port}`);
});
I print followings in a js,
console.log('LOCAL_TEST_ENVIRONMENT --- ', process.env.LOCAL_TEST_ENVIRONMENT) // LOCAL_TEST_ENVIRONMENT --- undefined
console.log('BACKEND_URL --- ', process.env.BACKEND_URL) // BACKEND_URL --- undefined
console.log('NODE_ENV --- ', process.env.NODE_ENV) // NODE_ENV --- production
Environment variables I set,
How can I fix this?

Answer 1

The prefix REACT_APP_ is necessary when accessing env variables, try
{process.env.REACT_APP_LOCAL_TEST_ENVIRONMENT}