title: How to detect changes in form control array in Angular 4?
body: <p>I am working on Angular 4 project. I have a requirement to detect the changes of form control array. e.g. I have a form control array named providers, how to detect its changes?</p>
  
  <pre><code>export class CustomFormArray {
   public form: FormGroup;
  
   constructor(private _fb: FormBuilder) {
        this.form = _fb.group({
             providers: _fb.array([])
        });
    }
  } 
  </code></pre>