isSubsetWith (Functional Programming)

Creates a function that checks subset membership using a custom equality function. Use it with pipe.

const result = pipe(array, isSubsetWith(superset, areItemsEqual));

::: info

Prefer the original es-toolkit isSubsetWith in ordinary code. Use this fp variant when composing transformations with pipe.

:::

Usage

isSubsetWith returns true when every value in the piped array matches at least one value in superset according to areItemsEqual.

import { isSubsetWith, pipe } from 'es-toolkit/fp';

pipe(
  [{ id: 1 }],
  isSubsetWith([{ id: 1 }, { id: 2 }], (a, b) => a.id === b.id)
); // => true

Parameters

• superset (readonly T[]): The array that may contain all values from the piped array.
• areItemsEqual ((item: T, other: T) => boolean): The function that decides whether two values are equal.

Returns

((array: readonly T[]) => boolean): A function that maps a readonly T[] to whether it is a subset.