MaxLengthValidator

A directive that adds max length validation to controls marked with the maxlength attribute. The directive is provided with the NG_VALIDATORS multi-provider list.

See also

• Form Validation

NgModules

• ReactiveFormsModule

• FormsModule

Selectors

• [maxlength][formControlName]
• [maxlength][formControl]
• [maxlength][ngModel]

Properties

Property	Description
@Input()maxlength: string	Tracks changes to the the maximum length bound to this directive.

Description

Adding a maximum length validator

The following example shows how to add a maximum length validator to an input attached to an ngModel binding.

<input name="firstName" ngModel maxlength="25">

Methods

ngOnChanges()
A lifecycle method called when the directive's inputs change. For internal use only.
ngOnChanges(changes: SimpleChanges): void Parameters changes SimpleChanges A object of key/value pairs for the set of changed inputs. Returns void

validate()
Method that validates whether the value exceeds the maximum length requirement.
validate(control: AbstractControl): ValidationErrors | null Parameters control AbstractControl Returns ValidationErrors | null

registerOnValidatorChange()
Registers a callback function to call when the validator inputs change.
registerOnValidatorChange(fn: () => void): void Parameters fn () => void The callback function Returns void