Validator interface

An interface implemented by classes that perform synchronous validation.

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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Interface

validate#

validate(control: AbstractControl): ValidationErrors|null

Method that performs synchronous validation against the provided control.

Returns A map of validation errors if validation fails, otherwise null.

registerOnValidatorChange#

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

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