title: Angular Subscribe valuechanges in formarray in form group
body: <p>I'm  angular8 and I have a form array inside of form group but I want to detect new changes of a certain input.</p>
  <pre><code>ngOnInit(): void {
      this.makeForm = this.fb.group({
  
       
        
        year:['', Validators.required],
        amount:['', Validators.required],
        desc:['', Validators.required],
        details: new FormArray([
          this.det(), 
        ])
      })
  
  
  det(){
        return new FormGroup({
          requestfor     : new FormControl(''),
          remarks        : new FormControl('')
      })}
  
  
  </code></pre>
  <p>I have to check the data that every value changes in formarray values. But I am getting error if I use</p>
  <pre><code>this.makeForm.value.details.get('requestfor').valueChanges
  
  </code></pre>
  <p>and the error is</p>
  <pre><code>ERROR TypeError: Cannot read property 'valueChanges' of undefined
  </code></pre>
  <p>how to get the value inside of form array value</p>
  <p>How to get the value.....</p>