Multiple Development Environments in React (CRA)

Multiple Development Environments in React (CRA)

Environment Variables in React

Environment variables are variables which are present outside the project and embedded into the project during build time. The CRA generates static HTML/CSS/JS bundles, hence it cannot read them at runtime.

Note: Environment variables are explained for React project created using create-react-app.

Benefits of Environment Variables

Hide Sensitive Information in Code

A project can have sensitive information which cannot be shared by another person and can be potentially misused. A few examples of sensitive information are secret or private keys for an API service like Firebase, MailJet and other services which can be used in the project.

Configure Multiple Development Environments

We require multiple environments like development, production, test, and UAT. Each environment can have a different configuration for various features like Database, deployment URL, and secret keys for various services.

Create Custom Environment Variables In .env

We can define the environment variables for react project by creating a .env file at the root of the project.

All the environment variables should always start with REACT_APP_, Otherwise it will be ignored.

Note: The development server must be restarted after changing the .env files. Similarly, the code needs to rebuild to update the build code with new environment configuration changes.

There is an example of a .env file.

  REACT_APP_PROJECT_TITLE = React Project - Dev

Access Environment Variables

HTML (public/index.html)

Add % before and after the environment variable name to access the value.


JavaScript / TypeScript (.js, .jsx, .ts, .tsx)

  const baseURL = process.env.REACT_APP_API_CLIENT_BASE_URL;

Variations of .env

The selection of environment files changes depending on the script used in React project. The priority of environment files decreases from left to right.

npm start

npm start runs the app in development mode.

.env.development.local, .env.local, .env.development, .env

npm run build

npm run build builds the app for production to the build folder.

.env.production.local, .env.local, .env.production, .env

npm test

npm test runs the app in test mode.

.env.test.local, .env.test, .env

Local variations of .env which are .env.local, .env.development.local, .env.test.local, .env.production.local should not be source controlled.

Custom Build Scripts for Other Environments

By now, we know that CRA provides to have development, production and testing.

Here are a few scenarios where you would need to create custom scripts.

  1. Configure a new environment which is not available in predefined variants.
  2. Choose which environment files to use to generate build code.
  3. Use a different name for the environment files other than the predefined variants.

This problem is solved by using an NPM package env-cm which allows the creation of scripts using an environment from a .env file.

Install env-cm NPM package

  npm i env-cmd

Create Environment Configuration for UAT

Let us assume I have a new environment called UAT. First, we have to create .env.uat file.


Create scripts in package.json

The command to run a script with a preferred environment file

The scripts in the below code snippet are used to create an optimized production build using the respective environment files.

  "build:production": "env-cmd -f .env.production react-scripts build",
"build:uat": "env-cmd -f .env.uat react-scripts build",

Generate Build Code for UAT environment

  npm run build:uat

Run build code

  npm install -g serve
serve -s build