How to show validation on button click in typescript

Question

I want to show up validation for the fields which are empty and for that i used the following method but its not working.Can anyone suggest me help.Thanks.

My template,<

Answer 1

Please check below solution.

DEMO : https://plnkr.co/edit/mJFftirG3ATDpnJRWmKN?p=preview

export class AppComponent {
  form: FormGroup;

  constructor(private formBuilder: FormBuilder){
      this.submitted=false;
       this.form = formBuilder.group({
        lastname: ['', Validators.required],
      });
   }

   onSubmit(form)
   {
      this.submitted=true;

      console.log(form);
      if(form.valid)    //<<<### submit form is it is valid only
      {
        console.log('form submitted');
      }
    }
}