Angular validators

angular-validators.ts

import {
  AbstractControl,
  AsyncValidatorFn,
  ValidationErrors,
  ValidatorFn,
  Validators,
} from '@angular/forms';

export class CustomValidators {
  
  /**
   * debounced async validator example
   * (async validators are the 3rd arg in FormControl constructor)
   */
  static nameValidator(existingName = ''): AsyncValidatorFn {
    return (control: AbstractControl): Observable<ValidationErrors> => {
      const val = control.value.trim();
      if (!val || val === existingName) {
        return of(null);
      } else {
        return timer(500).pipe(
          switchMap(() => this.service.nameIsAvailable(val)),
          map((result: boolean) => (result ? null : { nameTaken: true }))
        );
      }
    };
  }
      
  /**
   * regular custom validator
   */
  static nameValidator(): ValidatorFn {
    return (control: AbstractControl): ValidationErrors => {
      const name = control.value;
      if (name.length) {
        let valid = false;
        // do some validation here
        return valid ? null : { nameInvalid: true };
      }
      return null;
    };
  }

}