.env support for webpack - based on code from create-react-app

.env

# example of a config value
REACT_APP_EXAMPLE_VAL=1234

README.md

Add support for cascading .env files in webpapck project.

For documentation on which .env files can be used, see: https://facebook.github.io/create-react-app/docs/adding-custom-environment-variables#adding-development-environment-variables-in-env

env.js

// based on https://github.com/facebook/create-react-app/blob/master/packages/react-scripts/config/env.js

'use strict';

const fs = require('fs');
const path = require('path');

// originally from paths.js
const appDirectory = fs.realpathSync(process.cwd());
const resolveApp = relativePath => path.resolve(appDirectory, relativePath);

const paths = {
    dotenv: resolveApp('.env'),
}
// Make sure that including paths.js after env.js will read .env variables.
// delete require.cache[require.resolve('./paths')];

const NODE_ENV = process.env.NODE_ENV;
if (!NODE_ENV) {
  throw new Error(
    'The NODE_ENV environment variable is required but was not specified.'
  );
}

// https://github.com/bkeepers/dotenv#what-other-env-files-can-i-use
var dotenvFiles = [
  `${paths.dotenv}.${NODE_ENV}.local`,
  `${paths.dotenv}.${NODE_ENV}`,
  // Don't include `.env.local` for `test` environment
  // since normally you expect tests to produce the same
  // results for everyone
  NODE_ENV !== 'test' && `${paths.dotenv}.local`,
  paths.dotenv,
].filter(Boolean);

// Load environment variables from .env* files. Suppress warnings using silent
// if this file is missing. dotenv will never modify any environment variables
// that have already been set.
// https://github.com/motdotla/dotenv
dotenvFiles.forEach(dotenvFile => {
  if (fs.existsSync(dotenvFile)) {
    require('dotenv').config({
      path: dotenvFile,
    });
  }
});

// We support resolving modules according to `NODE_PATH`.
// This lets you use absolute paths in imports inside large monorepos:
// https://github.com/facebookincubator/create-react-app/issues/253.
// It works similar to `NODE_PATH` in Node itself:
// https://nodejs.org/api/modules.html#modules_loading_from_the_global_folders
// Note that unlike in Node, only *relative* paths from `NODE_PATH` are honored.
// Otherwise, we risk importing Node.js core modules into an app instead of Webpack shims.
// https://github.com/facebookincubator/create-react-app/issues/1023#issuecomment-265344421
// We also resolve them to make sure all tools using them work consistently.
// const appDirectory = fs.realpathSync(process.cwd());
process.env.NODE_PATH = (process.env.NODE_PATH || '')
  .split(path.delimiter)
  .filter(folder => folder && !path.isAbsolute(folder))
  .map(folder => path.resolve(appDirectory, folder))
  .join(path.delimiter);

// 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;

function getClientEnvironment(publicUrl) {
  const raw = Object.keys(process.env)
    .filter(key => REACT_APP.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,
      }
    );
  // 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 = getClientEnvironment;

webpack.config.js

const webpack = require('webpack');
const getClientEnvironment = require('./env');

// Read values from .env files
const publicUrl = '';
const env = getClientEnvironment(publicUrl);

// example for accessing a value in webpack config
const exampleVal = env.raw.REACT_APP_EXAMPLE_VAL;

const config = {
  // ...
  
  plugins: [
    //...,
    new webpack.DefinePlugin(env.stringified)
    //...,
  ]

  //...
};
  
module.exports = config;