Angular 6 FormGroup.disable() method is not working with my template driven NgForm

Question

When I try to use the disable method on a formGroup in my Angular 6 app , I get this error in the browser console :

TypeError: this.personForm.disable is not a function

Although the method is mentioned in the documentation & it is even suggested by VS Code as in this snapshot.

My code is here:

// ... many parts skipped, the form here is template driven 
// but still personForm is a FormGroup , 
// I am trying to disable the whole FormGroup with all child elements
@ViewChild('personForm') personForm: FormGroup;

        if (true) {
       // if I console.log here the form, I can see it is created already
         console.log(this.personForm);              
// output of console.log is 
// NgForm {submitted: false, _directives: Array(0), ngSubmit: EventEmitter, form: FormGroup}

         this.personForm.disable();
        }

What is the problem here ?

UPDATE 1:

I have created a stackblitz to show the issue

here is the link for that demo

UPDATE 2: As the error is not shown on initial loading, if you remove the this.firstStepForm.disable(); & rewrite it , you will get the error, but anyway the behavior is not correct, the form field is not disabled as expected

Also, refreshing the browser part in the stackblitz will show an error snackbar

Answer 1

I have discovered the reason for this error:

This form is made in the html template using ngForm, then I used ViewChild to get hold of the form in the typescript file, I noticed that I made that object of type FormGroup but ngForm is different than FormGroup (in my use cases it wasn't clear) that is why the FormGroup disable method is not working on the ngForm

Note:

(VS code is suggesting it as my type for that variable is FormGroup which is misleading the editor to give me that suggestion)

Thanks for everyone who tried to help.

Update:

In case someone is reluctant to depend on detectChanges() like me & Building upon the excellent Answer of Amit , we can disable the NgForm in this AfterContentChecked to avoid using detectChanges()

  // instead of disabling here & using cdr.detectChanges()

  // ngAfterViewChecked() {
  //     console.log(this.personForm.form);    
  //     this.personForm.form.disable(); 
  //     this.cdr.detectChanges();  
  // } 

  // we can put our disable here
  ngAfterContentChecked() {
    this.personForm.form.disable();
  }

Stackblitz demo