has-own-property

@sounisi5011/ts-type-util-has-own-property

Fix the type definition of the Object.prototype.hasOwnProperty() method.

Installation

npm install @sounisi5011/ts-type-util-has-own-property

yarn add @sounisi5011/ts-type-util-has-own-property

pnpm add @sounisi5011/ts-type-util-has-own-property

Usage

import { hasOwnProperty } from '@sounisi5011/ts-type-util-has-own-property';

const hasOwnProp = Object.prototype.hasOwnProperty.call as hasOwnProperty;

if (hasOwnProp(object, 'propertyName')) {
    // `object.propertyName` is available!
}

if ((Object.prototype.hasOwnProperty.call as hasOwnProperty)(object, 'propertyName')) {
    // `object.propertyName` is available!
}

Optional property

If an object has an optional property, it should not contain the type undefined. The hasOwnProperty type removes the undef type that is implicitly added from the value of an optional property.

import { hasOwnProperty } from '@sounisi5011/ts-type-util-has-own-property';

const hasOwnProp = Object.prototype.hasOwnProperty.call as hasOwnProperty;

// ----- //

interface Obj {
    prop?: string;
}

const obj: Obj = {};

if (hasOwnProp(obj, 'prop')) {
    // `obj.prop` is `string` type.
    // Not `string | undefined` type!
}

Optional property for union types with undefined

Since TypeScript 4.4, when the exactOptionalPropertyTypes option is enabled, optional properties are no longer union types by default. In this case, it is possible to specify the union type with undefined type as an optional property. The hasOwnProperty type will not remove the undefined type of a union type whose undefined type has been explicitly specified.

import { hasOwnProperty } from '@sounisi5011/ts-type-util-has-own-property';

const hasOwnProp = Object.prototype.hasOwnProperty.call as hasOwnProperty;

// ----- //

interface Obj {
    prop?: string | undefined;
}

const obj: Obj = {};

if (hasOwnProp(obj, 'prop')) {
    // If the `exactOptionalPropertyTypes` option is true, `obj.prop` is `string | undefined` type.
    // If the `exactOptionalPropertyTypes` option is false, `obj.prop` is `string` type.
}

Union type property with undefined

If it is not an optional property, the undefined type should not be removed. The hasOwnProperty type properly distinguishes between optional properties and the union types of other properties.

import { hasOwnProperty } from '@sounisi5011/ts-type-util-has-own-property';

const hasOwnProp = Object.prototype.hasOwnProperty.call as hasOwnProperty;

// ----- //

interface Obj {
    prop: string | undefined;
}

const obj: Obj = { prop: undefined };

if (hasOwnProp(obj, 'prop')) {
    // `obj.prop` is `string | undefined` type.
    // Not `string` type!
}

Non-existent property

We sometimes want to check for the existence of properties whose types are not defined. The hasOwnProperty type assumes that the value of a non-existent property is of type unknown.

import { hasOwnProperty } from '@sounisi5011/ts-type-util-has-own-property';

const hasOwnProp = Object.prototype.hasOwnProperty.call as hasOwnProperty;

// ----- //

const obj = {};

if (hasOwnProp(obj, 'hoge')) {
    // `obj.hoge` is `unknown` type.
}