title: How to watch on few fields changes in long form in Angular 2
body: <p>My form has 10 to 15 fields I just want to watch the changes on 2 fields built using form-builder.</p>
  
  <p>Currently i can watch all the fields in the form using the following code :</p>
  
  <pre><code>  export class App {
    constructor(private formBuilder: FormBuilder) {
      this.form = formBuilder.group({
        firstName: 'John',
        lastName: 'Fleming',
        Name: 'John Fleming',
        Address : '12331 wiley post',
        city: '',
        state:'',
        ...... so on    
      })
  
      this.form.valueChanges.subscribe(data =&gt; {
        console.log('Form changes', data)
        this.output = data
      })
    }
  }
  </code></pre>
  
  <p>I don't want to watch all the fields, I used (keyup) event on those fields to handle it for now. But I want to know whether there is any better way of doing the same in angular2?</p>