title: Call function on [hidden] change
body: <p>I have a component which i am showing/hiding using <code>[hidden]</code>. Within the component i want some code to run when the component is shown (when hidden is false).</p>
  
  <p>I've tried grabbing the input using <code>@Input() hidden: boolean</code> but this overrides the default behaviour. </p>
  
  <p>Is there a way of keeping the default functionality and still listen to the input?</p>