title: Fetching data in constructor
body: <p>Is a good practice to fetch data in javascript class <code>constructor()</code>? </p>
  
  <p>E.g. In react class <code>constructor()</code>, every tutorial which I find fetch data in <code>componendDidMount()</code>, but no one explein why We can't do it in <code>constructor()</code>.</p>
  
  <p>Question concerns javascript classes at all, not only <code>react</code>.  </p>