import { AbstractControl, ValidationErrors } from '@angular/forms'; import { userNameRegex } from '../../data-access/const/user-name-regex.const'; export function validateUsername( usernameControl: AbstractControl ): ValidationErrors | null { const value = usernameControl.value; const userName = new RegExp(userNameRegex); if (value && !userName.test(value)) { return { userNamePattern: true, }; } return null; }