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Teddy Zugana
Teddy Zugana

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NodeJS/ReactJS: Change HOST AND Port Number

By default, a ReactJS/ NodeJS app runs on port 3000. An Express.js app also runs on the same port 3000. If you were to run the two apps simultaneously, there would be conflicts. You need to change the port of one of them.

In ReactJS, the easiest way to alter the port number is by setting an environment variable named PORT to the desired number via the terminal. As an example, here we change the port number to 5000.

In Linux and Mac terminals, it would be

$export PORT=5000

In Windows, the command is slightly different


Next if you run

npm start

your local server will run on port 5000.
reactjs localhost port 5000

Modifying package.json

If your app is created via npx create-react-app, you will find the scripts property in your package.json file.

"scripts": {
"start": "react-scripts start",
"build": "react-scripts build",
"test": "react-scripts test --env=jsdom",
"eject": "react-scripts eject"

It has the start key and its value needs to be prepended with PORT=N, where N is the assigned port number. If you wish to run your React app on port number 2000, modify your package.json file as follows:

"scripts": {
"start": "HOST=IP ADDRESS PORT=2000 react-scripts start",
"build": "react-scripts build",
"test": "react-scripts test --env=jsdom",
"eject": "react-scripts eject"

Now if you run npm start, the app will start on port 2000.


Setting via .env

Port number can also be set as an environment variable. Create an .env file in the root directory of your project, i.e., in the same directory where the files .gitignore, package.json and are located.

Environment variables declared in the .env file are consumed in ReactJS as any local variable. An environment variable is defined on process.env. If you define an environment variable named IMG_PATH, it will be available in your component as process.env.IMG_PATH.

If you need the app to run on some port, assign an environment variable named PORT to the desired port number. Here, the port is assigned to the number 4000.


reactjs env port number

Save the .env file and do

npm start

The app will run on port 4000 and New HOST.

Top comments (1)

remo87 profile image

I'm getting this exception while running npm start 'HOST' is not recognized as an internal or external command, I've tried running it using powershell cmd and git bash