interface
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 }
validate() | |||
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Method that performs async validation against the provided control. | |||
|
control | AbstractControl | The control to validate against. |
Promise<ValidationErrors | null> | Observable<ValidationErrors | null>
: A promise or observable that resolves a map of validation errors if validation fails, otherwise null.
The following example implements the AsyncValidator
interface to create an async validator directive with a custom error key.
import { of } 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 of({'custom': true}); } }
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https://v12.angular.io/api/forms/AsyncValidator