Usage

const a = { a: 1, b: 2, c: 3 };

pick(a, ["a", "c"]); // => { a: 1, c: 3 }
pick(a, (value, key) => value > 1); // => { b: 2, c: 3 }

Installation

CLI

npx atmx add helper pick

Manually

Copy and paste the following method into @/utils/helpers/pick.ts:

type KeyOf<T extends object> = object extends T ? keyof any : keyof T;
type ValueOf<T extends object> = object extends T ? unknown : T[keyof T];

export type KeyFilterFunction<T extends object = object> = (
value: ValueOf<T>,
key: KeyOf<T>,
obj: T,
) => boolean;

/**
* Functions can use this type to accept either an array of keys or a
* filter function.
*/
export type KeyFilter<
T extends object = object,
Key extends keyof any = keyof any,
> = KeyFilterFunction<T> | readonly Key[];

/**
* Extract the keys of an object that pass a filter.
*/
export type FilteredKeys<
T extends object,
F extends KeyFilter<T> | null | undefined,
> = Extract<keyof T, F extends readonly any[] ? F[number] : any>;

import { isArray } from "@/helpers/is-array.ts";

/**
* Pick a list of properties from an object into a new object.
*
* ⚠️ When used with a predicate function, `pick` is potentially
* unsafe, because of partial type matching performed by TypeScript.
* If you pass an object with more properties than its TypeScript type
* has listed, the `value` and `key` parameter types of your callback
* will be inaccurate.
*
* @example
* const a = { a: 1, b: 2, c: 3 }
*
* pick(a, ['a', 'c']) // => { a: 1, c: 3 }
* pick(a, (value, key) => value > 1) // => { b: 2, c: 3 }
*/
export function pick<T extends object, F extends KeyFilter<T, keyof T>>(
obj: T,
filter: F,
): Pick<T, FilteredKeys<T, F>>;

export function pick<T extends object>(
obj: T,
filter: KeyFilter<T, keyof T> | null,
) {
if (!obj) {
return {};
}

let keys: (keyof T)[] = filter as any;

if (isArray(filter)) {
filter = null;
} else {
keys = Reflect.ownKeys(obj) as (keyof T)[];
}

return keys.reduce((acc, key) => {
const hasKey =
  Object.hasOwnProperty.call(obj, key) &&
  (filter == null || filter((obj as any)[key], key, obj));

if (hasKey) {
  acc[key] = obj[key];
}

return acc;
}, {} as T);
}