{
  "id": "api/forms/Validator",
  "title": "Validator",
  "contents": "\n\n<article>\n  <div class=\"breadcrumb-container\">\n    <div class=\"breadcrumb\">\n      <script type=\"application/ld+json\">\n        {\n          \"@context\": \"http://schema.org\",\n          \"@type\": \"BreadcrumbList\",\n          \"itemListElement\": [\n            { \"@type\": \"ListItem\", \"position\": 1, \"item\": { \"@id\": \"https://angular.io//api\", \"name\": \"API\" } },\n            { \"@type\": \"ListItem\", \"position\": 2, \"item\": { \"@id\": \"https://angular.io/api/forms\", \"name\": \"@angular/forms\" } },\n            { \"@type\": \"ListItem\", \"position\": 3, \"item\": { \"@id\": \"https://angular.io/api/forms/Validator\", \"name\": \"Validator\" } }\n          ]\n        }\n      </script>\n        <a href=\"/api\">API</a> > <a href=\"api/forms\">@angular/forms</a>\n    </div>\n    <div class=\"github-links\">\n  <a href=\"https://github.com/angular/angular/edit/master/packages/forms/src/directives/validators.ts?message=docs(forms)%3A%20describe%20your%20change...#L25-L70\" aria-label=\"Suggest Edits\" title=\"Suggest Edits\"><i class=\"material-icons\" aria-hidden=\"true\" role=\"img\">mode_edit</i></a>\n  <a href=\"https://github.com/angular/angular/tree/12.0.0-next.7/packages/forms/src/directives/validators.ts#L25-L70\" aria-label=\"View Source\" title=\"View Source\"><i class=\"material-icons\" aria-hidden=\"true\" role=\"img\">code</i></a>\n</div>\n  </div>\n  \n  <header class=\"api-header\">\n    <h1 id=\"validator\">Validator<a title=\"Link to this heading\" class=\"header-link\" aria-hidden=\"true\" href=\"api/forms/Validator#validator\"><i class=\"material-icons\">link</i></a></h1>\n    \n    <label class=\"api-type-label interface\">interface</label>\n    \n    \n    \n  </header>\n  \n  <aio-toc class=\"embedded\"></aio-toc>\n\n  <div class=\"api-body\">\n    \n  <section class=\"short-description\">\n    <p>An interface implemented by classes that perform synchronous validation.</p>\n\n    \n  </section>\n  \n  \n  <section class=\"interface-overview\">\n<code-example language=\"ts\" hidecopy=\"true\">\ninterface <a href=\"api/forms/Validator\" class=\"code-anchor\">Validator</a> {\n  <a class=\"code-anchor\" href=\"api/forms/Validator#validate\"><span class=\"member-name\">validate</span>(control: AbstractControl): ValidationErrors | null</a>\n  <a class=\"code-anchor\" href=\"api/forms/Validator#registerOnValidatorChange\"><span class=\"member-name\">registerOnValidatorChange</span>(fn: () => void)?: void</a>\n}\n</code-example>\n\n  \n  \n  <div class=\"descendants interface\">\n    <h2 id=\"child-interfaces\">Child interfaces<a title=\"Link to this heading\" class=\"header-link\" aria-hidden=\"true\" href=\"api/forms/Validator#child-interfaces\"><i class=\"material-icons\">link</i></a></h2>\n    \n\n<ul>\n  \n    <li>\n      <code><a href=\"api/forms/AsyncValidator\" class=\"code-anchor\">AsyncValidator</a></code>\n      \n\n\n    </li>\n  \n</ul>\n\n\n  </div>\n  \n\n\n  \n  \n  <div class=\"descendants class\">\n    <h2 id=\"class-implementations\">Class implementations<a title=\"Link to this heading\" class=\"header-link\" aria-hidden=\"true\" href=\"api/forms/Validator#class-implementations\"><i class=\"material-icons\">link</i></a></h2>\n    \n\n<ul>\n  \n    <li>\n      <code><a href=\"api/forms/EmailValidator\" class=\"code-anchor\">EmailValidator</a></code>\n      \n\n\n    </li>\n  \n    <li>\n      <code><a href=\"api/forms/MaxLengthValidator\" class=\"code-anchor\">MaxLengthValidator</a></code>\n      \n\n\n    </li>\n  \n    <li>\n      <code><a href=\"api/forms/MinLengthValidator\" class=\"code-anchor\">MinLengthValidator</a></code>\n      \n\n\n    </li>\n  \n    <li>\n      <code><a href=\"api/forms/PatternValidator\" class=\"code-anchor\">PatternValidator</a></code>\n      \n\n\n    </li>\n  \n    <li>\n      <code><a href=\"api/forms/RequiredValidator\" class=\"code-anchor\">RequiredValidator</a></code>\n      \n\n<ul>\n  \n    <li>\n      <code><a href=\"api/forms/CheckboxRequiredValidator\" class=\"code-anchor\">CheckboxRequiredValidator</a></code>\n      \n\n\n    </li>\n  \n</ul>\n\n\n    </li>\n  \n</ul>\n\n\n  </div>\n  \n\n</section>\n\n  \n\n  \n  \n  \n\n  \n\n<section class=\"instance-methods\">\n  <h2 id=\"methods\">Methods<a title=\"Link to this heading\" class=\"header-link\" aria-hidden=\"true\" href=\"api/forms/Validator#methods\"><i class=\"material-icons\">link</i></a></h2>\n  \n    <a id=\"validate\"></a>\n<table class=\"is-full-width method-table instance-method\">\n  <thead><tr><th>\n    <div class=\"with-github-links\">\n    <h3 id=\"validate\">\n      validate()\n      \n    <a title=\"Link to this heading\" class=\"header-link\" aria-hidden=\"true\" href=\"api/forms/Validator#validate\"><i class=\"material-icons\">link</i></a></h3>\n    <div class=\"github-links\">\n  <a href=\"https://github.com/angular/angular/edit/master/packages/forms/src/directives/validators.ts?message=docs(forms)%3A%20describe%20your%20change...#L52-L61\" aria-label=\"Suggest Edits\" title=\"Suggest Edits\"><i class=\"material-icons\" aria-hidden=\"true\" role=\"img\">mode_edit</i></a>\n  <a href=\"https://github.com/angular/angular/tree/12.0.0-next.7/packages/forms/src/directives/validators.ts#L52-L61\" aria-label=\"View Source\" title=\"View Source\"><i class=\"material-icons\" aria-hidden=\"true\" role=\"img\">code</i></a>\n</div>\n    </div>\n  </th></tr></thead>\n  <tbody>\n    <tr>\n      <td class=\"short-description\">\n        <p>Method that performs synchronous validation against the provided control.</p>\n\n      </td>\n    </tr>\n  \n    <tr>\n      <td>\n        <div class=\"overload-info\">\n  \n\n  <code-example language=\"ts\" hidecopy=\"true\" class=\"no-box api-heading\"><span class=\"member-name\">validate</span>(control: <a href=\"api/forms/AbstractControl\" class=\"code-anchor\">AbstractControl</a>): <a href=\"api/forms/ValidationErrors\" class=\"code-anchor\">ValidationErrors</a> | null</code-example>\n\n  \n\n  <h6 class=\"no-anchor\" id=\"parameters\">Parameters</h6>\n  <table class=\"is-full-width list-table parameters-table instance-method-overload-parameters\">\n  <tbody>\n  \n    <tr class=\"instance-method-overload-parameter\">\n      <td class=\"param-name\">\n        <a id=\"\"></a>\n        <code>control</code>\n      </td>\n      <td class=\"param-type\"><code><a href=\"api/forms/AbstractControl\" class=\"code-anchor\">AbstractControl</a></code></td>\n      <td class=\"param-description\">\n      <p>The control to validate against.</p>\n\n      </td>\n    </tr>\n  </tbody>\n</table>\n\n  \n  <h6 class=\"no-anchor\" id=\"returns\">Returns</h6>\n  <p><code><a href=\"api/forms/ValidationErrors\" class=\"code-anchor\">ValidationErrors</a> | null</code>: A map of validation errors if validation fails,\notherwise null.</p>\n\n  \n\n\n  \n\n  \n</div>\n      </td>\n    </tr>\n  \n\n  \n\n  \n    </tbody>\n</table>\n\n  \n    <a id=\"registerOnValidatorChange\"></a>\n<table class=\"is-full-width method-table instance-method\">\n  <thead><tr><th>\n    <div class=\"with-github-links\">\n    <h3 id=\"registeronvalidatorchange\">\n      registerOnValidatorChange()\n      \n    <a title=\"Link to this heading\" class=\"header-link\" aria-hidden=\"true\" href=\"api/forms/Validator#registeronvalidatorchange\"><i class=\"material-icons\">link</i></a></h3>\n    <div class=\"github-links\">\n  <a href=\"https://github.com/angular/angular/edit/master/packages/forms/src/directives/validators.ts?message=docs(forms)%3A%20describe%20your%20change...#L62-L69\" aria-label=\"Suggest Edits\" title=\"Suggest Edits\"><i class=\"material-icons\" aria-hidden=\"true\" role=\"img\">mode_edit</i></a>\n  <a href=\"https://github.com/angular/angular/tree/12.0.0-next.7/packages/forms/src/directives/validators.ts#L62-L69\" aria-label=\"View Source\" title=\"View Source\"><i class=\"material-icons\" aria-hidden=\"true\" role=\"img\">code</i></a>\n</div>\n    </div>\n  </th></tr></thead>\n  <tbody>\n    <tr>\n      <td class=\"short-description\">\n        <p>Registers a callback function to call when the validator inputs change.</p>\n\n      </td>\n    </tr>\n  \n    <tr>\n      <td>\n        <div class=\"overload-info\">\n  \n\n  <code-example language=\"ts\" hidecopy=\"true\" class=\"no-box api-heading\"><span class=\"member-name\">registerOnValidatorChange</span>(fn: () => void)?: void</code-example>\n\n  \n\n  <h6 class=\"no-anchor\" id=\"parameters-1\">Parameters</h6>\n  <table class=\"is-full-width list-table parameters-table instance-method-overload-parameters\">\n  <tbody>\n  \n    <tr class=\"instance-method-overload-parameter\">\n      <td class=\"param-name\">\n        <a id=\"\"></a>\n        <code>fn</code>\n      </td>\n      <td class=\"param-type\"><code>() => void</code></td>\n      <td class=\"param-description\">\n      <p>The callback function</p>\n\n      </td>\n    </tr>\n  </tbody>\n</table>\n\n  \n  <h6 class=\"no-anchor\" id=\"returns-1\">Returns</h6>\n  <p><code>void</code></p>\n\n  \n\n\n  \n\n  \n</div>\n      </td>\n    </tr>\n  \n\n  \n\n  \n    </tbody>\n</table>\n\n  \n</section>\n\n\n  \n<section class=\"usage-notes\">\n  <h2 id=\"usage-notes\">Usage notes<a title=\"Link to this heading\" class=\"header-link\" aria-hidden=\"true\" href=\"api/forms/Validator#usage-notes\"><i class=\"material-icons\">link</i></a></h2>\n  <h3 id=\"provide-a-custom-validator\">Provide a custom validator<a title=\"Link to this heading\" class=\"header-link\" aria-hidden=\"true\" href=\"api/forms/Validator#provide-a-custom-validator\"><i class=\"material-icons\">link</i></a></h3>\n<p>The following example implements the <code><a href=\"api/forms/Validator\" class=\"code-anchor\">Validator</a></code> interface to create a\nvalidator directive with a custom error key.</p>\n<code-example language=\"typescript\">\n@<a href=\"api/core/Directive\" class=\"code-anchor\">Directive</a>({\n  selector: '[customValidator]',\n  providers: [{provide: <a href=\"api/forms/NG_VALIDATORS\" class=\"code-anchor\">NG_VALIDATORS</a>, useExisting: CustomValidatorDirective, multi: true}]\n})\nclass CustomValidatorDirective implements <a href=\"api/forms/Validator\" class=\"code-anchor\">Validator</a> {\n  validate(control: <a href=\"api/forms/AbstractControl\" class=\"code-anchor\">AbstractControl</a>): <a href=\"api/forms/ValidationErrors\" class=\"code-anchor\">ValidationErrors</a>|null {\n    return {'custom': true};\n  }\n}\n</code-example>\n\n</section>\n\n\n\n  </div>\n</article>\n\n<!-- links to this doc:\n - api/forms\n - api/forms/AsyncValidator\n - api/forms/NG_ASYNC_VALIDATORS\n - api/forms/NG_VALIDATORS\n - guide/form-validation\n-->\n<!-- links from this doc:\n - /api\n - api/core/Directive\n - api/forms\n - api/forms/AbstractControl\n - api/forms/AsyncValidator\n - api/forms/CheckboxRequiredValidator\n - api/forms/EmailValidator\n - api/forms/MaxLengthValidator\n - api/forms/MinLengthValidator\n - api/forms/NG_VALIDATORS\n - api/forms/PatternValidator\n - api/forms/RequiredValidator\n - api/forms/ValidationErrors\n - api/forms/Validator#child-interfaces\n - api/forms/Validator#class-implementations\n - api/forms/Validator#methods\n - api/forms/Validator#provide-a-custom-validator\n - api/forms/Validator#registerOnValidatorChange\n - api/forms/Validator#registeronvalidatorchange\n - api/forms/Validator#usage-notes\n - api/forms/Validator#validate\n - api/forms/Validator#validator\n - https://github.com/angular/angular/edit/master/packages/forms/src/directives/validators.ts?message=docs(forms)%3A%20describe%20your%20change...#L25-L70\n - https://github.com/angular/angular/edit/master/packages/forms/src/directives/validators.ts?message=docs(forms)%3A%20describe%20your%20change...#L52-L61\n - https://github.com/angular/angular/edit/master/packages/forms/src/directives/validators.ts?message=docs(forms)%3A%20describe%20your%20change...#L62-L69\n - https://github.com/angular/angular/tree/12.0.0-next.7/packages/forms/src/directives/validators.ts#L25-L70\n - https://github.com/angular/angular/tree/12.0.0-next.7/packages/forms/src/directives/validators.ts#L52-L61\n - https://github.com/angular/angular/tree/12.0.0-next.7/packages/forms/src/directives/validators.ts#L62-L69\n-->"
}