index.js

// Adapted from create-react-app. Copied their initial Environment Variables
// https://github.com/facebook/create-react-app/blob/26a1c7f6b38fe7119a8fd92d10eb63597376d7de/packages/react-scripts/config/env.js

// Populates process.env from RELEASE_ environment variables
function getReleaseEnvironmentVariables() {
  const RELEASE = /^RELEASE_/i;

  const raw = Object.keys(process.env)
  .filter(key => {
    return RELEASE.test(key)
  }).reduce(
    (env, key) => {
      env[key] = process.env[key];
      return env;
    }, 
    {
      // 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,
      // We support configuring the sockjs pathname during development.
      // These settings let a developer run multiple simultaneous projects.
      // They are used as the connection `hostname`, `pathname` and `port`
      // in webpackHotDevClient. They are used as the `sockHost`, `sockPath`
      // and `sockPort` options in webpack-dev-server.
      WDS_SOCKET_HOST: process.env.WDS_SOCKET_HOST,
      WDS_SOCKET_PATH: process.env.WDS_SOCKET_PATH,
      WDS_SOCKET_PORT: process.env.WDS_SOCKET_PORT,
      // Whether or not react-refresh is enabled.
      // react-refresh is not 100% stable at this time,
      // which is why it's disabled by default.
      // It is defined here so it is available in the webpackHotDevClient.
      FAST_REFRESH: process.env.FAST_REFRESH || false,
    }
  )

  // Stringify all values so we can feed into webpack DefinePlugin
  const stringified = {
    'process.env': Object.keys(raw).reduce((env, key) => {
      env[key] = JSON.stringify(raw[key]);
      return env;
    }, {}),
  };

  return { raw, stringified }
}

module.exports = getReleaseEnvironmentVariables;