AsyncValidator

interface

Contents

An interface implemented by classes that perform asynchronous validation.

      
      interface AsyncValidator extends Validator {
  validate(control: AbstractControl): Promise<ValidationErrors | null> | Observable<ValidationErrors | null>

  // inherited from forms/Validator
  validate(control: AbstractControl): ValidationErrors | null
  registerOnValidatorChange(fn: () => void)?: void
}

Methods

validate()

Method that performs async validation against the provided control.

      
      validate(control: AbstractControl): Promise<ValidationErrors | null> | Observable<ValidationErrors | null>

Parameters

control

AbstractControl

The control to validate against.

Returns

Promise<ValidationErrors | null> | Observable<ValidationErrors | null>: A promise or observable that resolves a map of validation errors if validation fails, otherwise null.

Usage notes

Provide a custom async validator directive

The following example implements the AsyncValidator interface to create an async validator directive with a custom error key.

      
      import { of as observableOf } from 'rxjs';
 
@Directive({
  selector: '[customAsyncValidator]',
  providers: [{provide: NG_ASYNC_VALIDATORS, useExisting: CustomAsyncValidatorDirective, multi:
true}]
})
class CustomAsyncValidatorDirective implements AsyncValidator {
  validate(control: AbstractControl): Observable<ValidationErrors|null> {
    return observableOf({'custom': true});
  }
}