Validator - Angular

An interface implemented by classes that perform synchronous validation.

API

interface Validator {
  validate(control: AbstractControl<any, any, any>): ValidationErrors | null;
  optional registerOnValidatorChange(fn: () => void): void;
}

validate

ValidationErrors | null

Method that performs synchronous validation against the provided control.

@paramcontrolAbstractControl<any, any, any>

The control to validate against.

@returnsValidationErrors | null

registerOnValidatorChange

void

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

@paramfn() => void

The callback function

@returnsvoid

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: forwardRef(() => CustomValidatorDirective), multi: true}]
})
class CustomValidatorDirective implements Validator {
  validate(control: AbstractControl): ValidationErrors|null {
    return {'custom': true};
  }
}