title: Angular4 mandatory Input on component
body: <p>I've a component with the following input</p>
  
  <pre><code>@Input() id: string
  </code></pre>
  
  <p>I would like this input to be mandatory, which means that if I call my component without specifying it, it would throw a js error.</p>
  
  <p>I can do it in the <code>ngOnInit</code>, but I imagine there is a keyword for this ?</p>