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Validator

interface

An interface implemented by classes that perform synchronous validation.

interface Validator {
  validate(control: AbstractControl): ValidationErrors | null
  registerOnValidatorChange(fn: () => void)?: void
}

Child interfaces

Methods

Method that performs synchronous validation against the provided control.

validate(control: AbstractControl): ValidationErrors | null

Parameters
control AbstractControl

The control to validate against.

Returns

ValidationErrors | null: A map of validation errors if validation fails, otherwise null.

Registers a callback function to call when the validator inputs change.

registerOnValidatorChange(fn: () => void)?: void

Parameters
fn () => void

The callback function

Returns

void

Usage notes

Provide a custom validator

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

@Directive({
  selector: '[customValidator]',
  providers: [{provide: NG_VALIDATORS, useExisting: CustomValidatorDirective, multi: true}]
})
class CustomValidatorDirective implements Validator {
  validate(control: AbstractControl): ValidationErrors|null {
    return {'custom': true};
  }
}

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Licensed under the Creative Commons Attribution License 4.0.
https://angular.io/api/forms/Validator