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.