Dynamically addControl to formgroup Angular 5

Sure, but the second parameters should be a FormControl instance. Something like:

this.testForm.addControl('new', new FormControl('', Validators.required));

You can also add the validators dynamically if you want with the setValidators method.

More information here: https://angular.io/api/forms/FormGroup#addControl

If you are using FormBuilder for your form, you can also use that for adding a control:

constructor(private fb: FormBuilder) { }
    
method() {
  this.testForm.addControl('new', this.fb.control('', Validators.required));
}

simple use:

  this.testForm.addControl('new', this.fb.group({
      name: ['', Validators.required]
    }));

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