title: Angular 6 how do I track changes to form fields after certain interval
body: <p>I have few forms fields in the smart component  and some in the child component.
  and I have a print and submit button.</p>
  
  <p>user enters all the fields and clicks Print button, if print is successful only then submit button will be enabled.The submit button will be disabled if validation fails on any fields too.</p>
  
  <p>after successful print--
  1) Suppose if the user changes anything in any of the fields I want to disable the button --this is  OK I can use @Input and @Output to track changes by EVENT EMitter and method calls(IS there a better way to do it please??)
  2) If user reverts his changes back to the original values, the way they were after the print, I want to enable the submit button?? How do I do this??</p>