title: How to get FormControlName of the field which value changed in Angular reactive forms
body: <p>I have a reactive form with over 10 form controls and using subscription on valueChanges observable to detect changes. It works perfectly but output is always the entire form value object(meaning all the form controls and their values). Is there a way to simply get the form control name of the field that changed?</p>
  
  <pre><code>this.form = this.fb.group({
      field1: ['', Validators.required],
      field2: ['', Validators.required],
      field3: ['', Validators.required],
      field4: ['', Validators.required],
      field5: ['', Validators.required],
      field6: ['', Validators.required],
      field7: ['', Validators.required],
      field8: ['', Validators.required],
      field9: ['', Validators.required],
      field10: ['', Validators.required],
      field11: ['', Validators.required],
      field12: ['', Validators.required],
      field13: [{ value: '', disabled: true }, Validators.required]
  });
  
  this.form.valueChanges.subscribe(
      result =&gt; this.calculateParams(result)
  );
  
  calculateParams(result) {
      console.log(result); // giving the entire form.value object
  }
  </code></pre>