ReactJS + Environment Variables

If you are using create-react-app, you will need to update your env.js to include your new environment variable in the build.

The function getClientEnvironment(publicUrl) sets the environment variables that get injected into the build for your use. Here, you can add your custom env variable like so:

  {
    // Useful for determining whether we’re running in production mode.
    // Most importantly, it switches React into the correct mode.
    NODE_ENV: process.env.NODE_ENV || 'development',
    // Useful for resolving the correct path to static assets in `public`.
    // For example, <img src={process.env.PUBLIC_URL + '/img/logo.png'} />.
    // This should only be used as an escape hatch. Normally you would put
    // images into the `src` and `import` them in code to get their paths.
    PUBLIC_URL: publicUrl,
    CUSTOM: process.env.CUSTOM || 'fallback'
  }

UPDATE:

If you're not using CRA, you can use the webpack DefinePlugin to do the same thing.

UPDATE 2:

@DimitarChristoff pointed out that you should use the REACT_APP_* format for declaring env variables. If you prepend your env variable with REACT_APP_, CRA will automatically pick it up and add it to the Webpack DefinePlugin:

// Grab NODE_ENV and REACT_APP_* environment variables and prepare them to be
// injected into the application via DefinePlugin in Webpack configuration.
const REACT_APP = /^REACT_APP_/i;

It was more simple than expected. The .env files has to be placed in the root of the project NOT in the SRC folder.

That's all!

In general Webpack case, you can use webpack's DefinePlugin to define variables to be accessible across app.

In CRA (Create-React-App), you can add the environment variable in env.js file.

Using env.js is same as making your own config.js file where you create your config variable with a value either from process.env or use a default.