intersectionBy (Functional Programming)

Creates a function that keeps values by a mapped key. Use it with pipe.

const result = pipe(array, intersectionBy(secondArray, mapper));

::: info

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

:::

Usage

intersectionBy compares the values returned by mapper. Values from the piped array are kept when their mapped key appears in secondArray.

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

pipe(
  [{ id: 1 }, { id: 2 }],
  intersectionBy([2], value => (typeof value === 'number' ? value : value.id))
); // => [{ id: 2 }]

Parameters

• secondArray (readonly U[]): The array containing values whose mapped keys should be kept.
• mapper ((item: T | U) => unknown): The function that returns the comparison key.

Returns

((array: readonly T[]) => T[]): A function that maps a readonly T[] to values whose keys are found in secondArray.