{ "id": "api/forms/AsyncValidator", "title": "AsyncValidator", "contents": "\n\n
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AsyncValidatorlink

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An interface implemented by classes that perform asynchronous validation.

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\n\ninterface AsyncValidator extends Validator {\n validate(control: AbstractControl): Promise<ValidationErrors | null> | Observable<ValidationErrors | null>\n\n // inherited from forms/Validator\n validate(control: AbstractControl): ValidationErrors | null\n registerOnValidatorChange(fn: () => void)?: void\n}\n\n\n \n \n\n\n \n \n\n
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Methodslink

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\n validate()\n \n link

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Method that performs async validation against the provided control.

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\n \n\n validate(control: AbstractControl): Promise<ValidationErrors | null> | Observable<ValidationErrors | null>\n\n \n\n
Parameters
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\n \n control\n AbstractControl\n

The control to validate against.

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Returns
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Promise<ValidationErrors | null> | Observable<ValidationErrors | null>: A promise or observable that resolves a map of validation errors\nif validation fails, otherwise null.

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Usage noteslink

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Provide a custom async validator directivelink

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The following example implements the AsyncValidator interface to create an\nasync validator directive with a custom error key.

\n\nimport { of } from 'rxjs';\n\n@Directive({\n selector: '[customAsyncValidator]',\n providers: [{provide: NG_ASYNC_VALIDATORS, useExisting: CustomAsyncValidatorDirective, multi:\ntrue}]\n})\nclass CustomAsyncValidatorDirective implements AsyncValidator {\n validate(control: AbstractControl): Observable<ValidationErrors|null> {\n return of({'custom': true});\n }\n}\n\n\n
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\n\n\n" }