title: Angular: Deep copy a reactive form
body: <p>I need to make a deep copy of a reactive form.
  I have tried with ES6 spread syntax for cloning a form. I have used Typescript generics to typecast the return value of the spread syntax to <code>FormGroup</code>. Also, the type of clone form variable is set to <code>FormGroup</code>.</p>
  
  <p>But when the form is cloned by this way, the type is lost on the cloned form variable, that is, it is no longer of type of <code>FormGroup</code>. So, the cloned form is not usable.</p>
  
  <p>Here is the stackblitz for the same: <a href="https://stackblitz.com/edit/angular-a2pfwp" rel="nofollow noreferrer">form cloning</a></p>
  
  <p>What is going wrong in above way of cloning? Why the type <code>FormGroup</code> is lost on the cloned form?</p>