config/env.js

// Copyright (c) 2017 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

// Grab NODE_ENV and REACT_APP_* environment variables and prepare them to be
// injected into the application via DefinePlugin in Webpack configuration.

var REACT_APP = /^REACT_APP_/i;

function getClientEnvironment(publicUrl) {
  return Object
    .keys(process.env)
    .filter(key => REACT_APP.test(key))
    .reduce((env, key) => {
      env['process.env.' + key] = JSON.stringify(process.env[key]);
      return env;
    }, {
      // Useful for determining whether we’re running in production mode.
      // Most importantly, it switches React into the correct mode.
      'process.env.NODE_ENV': JSON.stringify(
        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.
      'process.env.PUBLIC_URL': JSON.stringify(publicUrl)
    });
}

module.exports = getClientEnvironment;