title: env variable in JSON file in public folder of CRA
body: <p>I have this <code>config.json</code> file located in my public folder, in which I need to put some params different in development and in production modes. I fetch it when my app loads (<code>fetch('config.json').then()</code>).</p>
  
  <p>Is there a way that my <code>config.json</code> file looks like that : </p>
  
  <pre><code>{
    "url": "%REACT_APP_URL%"
  }
  </code></pre>
  
  <p>Of course, the code above doesn't work : is there another solution ?</p>