title: React create constants file
body: <p>How to create constants file like: key - value in ReactJs,</p>
  
  <pre><code>ACTION_INVALID = "This action is invalid!"
  </code></pre>
  
  <p>and to use that in other components</p>
  
  <pre><code>errorMsg = myConstClass.ACTION_INVALID;
  </code></pre>