create-react-app's dotenv resolution as a babel plugin.

The environment variables from .env files are embedded using babel. These environment variables are defined for you on process.env.

NODE_ENV is also embedded and must be one of production, test, or development, defaulting to development in all other cases.

Adding Development Environment Variables In .env

To define permanent environment variables, create a file called .env in the root of your project:

SECRET_CODE=abcdef

Changing any environment variables will require you to restart the development server if it is running.

.env files should be checked into source control (with the exclusion of .env*.local).

What other .env files can be used?

• .env: Default.
• .env.local: Local overrides. This file is loaded for all environments except test.
• .env.development, .env.test, .env.production: Environment-specific settings.
• .env.development.local, .env.test.local, .env.production.local: Local overrides of environment-specific settings.

Files on the left have more priority than files on the right:

• npm start: .env.development.local, .env.development, .env.local, .env
• npm run build: .env.production.local, .env.production, .env.local, .env
• npm test: .env.test.local, .env.test, .env (note .env.local is missing)

These variables will act as the defaults if the machine does not explicitly set them. Please refer to the dotenv documentation for more details.

Note: If you are defining environment variables for development, your CI and/or hosting platform will most likely need these defined as well. Consult their documentation how to do this. For example, see the documentation for Travis CI or Heroku.

Expanding Environment Variables In .env

Note: this feature is available with [email protected] and higher.

Expand variables already on your machine for use in your .env file (using dotenv-expand).

For example, to get the environment variable npm_package_version:

VERSION=$npm_package_version
# also works:
# VERSION=${npm_package_version}

Or expand variables local to the current .env file:

DOMAIN=www.example.com
FOO=$DOMAIN/foo
BAR=$DOMAIN/bar

Comparison with other packages

• create-react-app is the inspiration for this package. This plugin is unnecessary when using create-react-app, but brings the same functionality to other contexts.
• universal-dotenv was another inspiration. It modifies the rules from create-react-app to be universal. It needs to be requireed or imported in the application entry point or webpack can use DefinePlugin. This plugin aims to bring similar functionality to babel. We consciously avoided the prefixing logic due to the environment variable leakage being less of an issue in a server-side context.