ts-data-forge
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[](https://www.npmjs.com/package/ts-data-forge) [](https://www.npmjs.com/package/ts-data-forge) [ • 1.54 kB
JavaScript
/**
* Type guard that checks if a key exists as an own property in an object.
*
* This function is similar to `hasKey()` but with reversed parameter order and
* different type narrowing behavior. While `hasKey()` narrows the object type,
* `keyIsIn()` narrows the key type to be a valid key of the given object.
*
* **Type Narrowing Behavior:**
*
* - Narrows the key type to be a key that exists in the object (`K & keyof R`)
* - Useful when you have a dynamic key and want to ensure it's valid for a
* specific object
* - The object type remains unchanged
*
* **Implementation:** Uses `Object.hasOwn()` to check for own properties (not
* inherited).
*
* @example
*
* ```ts
* const user = { id: 1, name: 'Ada' } as const;
*
* const maybeKey: string = 'name';
*
* if (keyIsIn(maybeKey, user)) {
* assert.isTrue(user[maybeKey] === 'Ada');
* } else {
* assert.fail();
* }
* ```
*
* @template K - The type of the key to check, must extend PropertyKey (string |
* number | symbol)
* @template R - The type of the record (object), must extend UnknownRecord
* @param key - The key to check for
* @param obj - The object to check within
* @returns `true` if `key` is an own property of `obj`, `false` otherwise. When
* `true`, TypeScript narrows the key type to be a valid key of the object.
* @see {@link hasKey} - Similar function that narrows the object type instead of the key type
*/
const keyIsIn = (key, obj) => Object.hasOwn(obj, key);
export { keyIsIn };
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