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

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

export function URLFormatValidator(control: AbstractControl): {[key: string]: any} | null {
  const valid = /^(?:http(s)?:\/\/)?[\w.-]+(?:\.[\w\.-]+)+[\w\-\._~:/?#[\]@!\$&'\(\)\*\+,;=.]+$/.test(control.value);
  return valid ? null : {'invalidURLFormat': {value: control.value}};
}