Usage

select(
  [1, 2, 3, 4],
  (x) => x * x,
  (x) => x > 2,
); // => [9, 16]

Installation

CLI

npx atmx add helper select

Manually

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

/**
* Select performs a filter and a mapper inside of a reduce, only
* iterating the list one time. If condition is omitted, will
* select all mapped values that are non-nullish.
*
* @example
* select(
*   [1, 2, 3, 4],
*   x => x * x,
*   x => x > 2
* ) // => [9, 16]
*/
export function select<T, U>(
array: readonly T[],
mapper: (item: T, index: number) => U,
condition: ((item: T, index: number) => boolean) | null | undefined,
): U[];

export function select<T, U>(
array: readonly T[],
mapper: (item: T, index: number) => U | null | undefined,
): U[];

export function select<T, U>(
array: readonly T[],
mapper: (item: T, index: number) => U,
condition?: ((item: T, index: number) => boolean) | null,
): U[] {
if (!array) {
return [];
}
let mapped: U;

return array.reduce((acc, item, index) => {
if (condition) {
  condition(item, index) && acc.push(mapper(item, index));
} else if ((mapped = mapper(item, index)) != null) {
  acc.push(mapped);
}

return acc;
}, [] as U[]);
}