Use Case

While developing a web application most of the developers use Create React App. This means that once you start creating a build, it gets created for a specific environment and continues to exist in the same environment.

"scripts": {
    "start": "node scripts/start.js",
    "build": "node scripts/build.js",
    "test": "node scripts/test.js"
  }

Developers can only use two environments by default.

• Development — NODE_ENV=development when developing the application locally. Uses .env.development by default, if available.

• Production — NODE_ENV=production when building the application for deployment. Uses .env.production by default, if available.

Imagine my project has four environments:

• Development
• Testing
• Staging
• Production

Suppose you have different API URL for each environment or APPINSIGHTS_KEY which can used for the analytics. You can add the configuration in the .env file. Below are the files which we can used for different environments.

.env.development
REACT_APP_BASE_API_URL = 'https://learning.int.org/'

.env.qa
REACT_APP_BASE_API_URL = 'https://learning.qa.org/'

.env.candidate
REACT_APP_BASE_API_URL = 'https://learning.candidate.org/'

.env.production
REACT_APP_BASE_API_URL = 'https://learning.production.org/'

Note: Prefix “REACT_APP_” is required for creating custom variables in React.

Now we need to change the build script in package.json file.

"scripts": {
    "start-js": "run-s react:start lint",
    "react:start": "react-scripts start",
    "start:development": "env-cmd -f .env.development npm run-script start-js",
    "build:integration": "env-cmd -f .env.integration npm run-script build",
    "build:qa": "env-cmd -f .env.qa npm run-script build",
    "build:candidate": "env-cmd -f .env.candidate npm run-script build",
    "build:production": "env-cmd -f .env.production npm run-script build",
    "build": "set \"GENERATE_SOURCEMAP=false\" && rimraf ./build && react-scripts build",
  }

Access the variables in-app : process.env.REACT_APP_BASE_API_URL

Note: Though we have added four different environments and when you build the app NODE_ENV will be production. To distinguish the builds, you can add REACT_APP_ENV and specify your environment there.

Hope this article solves some of the problems that occur on day to day basis.