title: Setting environment variable in react-native?
body: <p>I am using react-native to build a cross-platform app, but I do not know how to set the environment variable so that I can have different constants for different environments.</p>
  
  <p>Example:</p>
  
  <pre><code>development: 
    BASE_URL: '',
    API_KEY: '',
  staging: 
    BASE_URL: '',
    API_KEY: '',
  production:
    BASE_URL: '',
    API_KEY: '',
  </code></pre>