web-application-engineering/frontend/src/app/validators/keywords.validator.ts

import {AbstractControl} from '@angular/forms';

export function keywordsValidator(control: AbstractControl): { [key: string]: any } | null {
  const valid = /^((\w){3,},?){1,2}(\w{3,})?$/.test(control.value);
  return valid ? null : {'invalidKeywords': {value: control.value}};
}