Angular 4 remove required validator conditionally

if you want to add validation try this one.

saveDraft() {
   this.form.get('title').setValidators([Validators.required, Validators.minLength(3)]);
   this.form.get('title').updateValueAndValidity();
}

if you want to remove validators try this one.

saveDraft() {
 this.form.get('title').clearValidators();
 this.form.get('title').updateValueAndValidity();
}