title: React-native : detect dev or production env
body: <p>I develop a react-native app where some API calls should be made.</p>
  
  <p>If I'm in production mode my app should call, for example, this host :</p>
  
  <pre><code>https://example.com/
  </code></pre>
  
  <p>but if I'm in dev mode, it should call my local host machine on a different port, for example :</p>
  
  <pre><code>http://192.168.0.10:8080/
  </code></pre>
  
  <p>How the react-native code can be aware of its environment ?</p>
  
  <p><code>.dotenv</code> seems to not work with react-native.</p>
  
  <p>In the Chrome debug, we can see that the application is launched with some params :</p>
  
  <pre><code>Running application "AppName" with appParams: {"initialProps":{},"rootTag":1}. __DEV__ === true, development-level warning are ON, performance optimizations are OFF
  </code></pre>
  
  <p>Can we get this <code>__DEV__</code> value in the application ?</p>
  
  <p>Thanks</p>