es-toolkit/docs/reference/array/unionBy.md

unionBy

Creates an array of unique values, in order, from all given arrays using a provided mapping function to determine equality.

Signature

function unionBy<T, U>(arr1: T[], arr2: T[], mapper: (item: T) => U): T[];

Parameters

• arr1 (T[]): The first array.
• arr2 (U[]): The second array.
• mapper: ((item: T) => U): The function to map array elements to comparison values.

Returns

(T[]): A new array containing the union of unique elements from arr1 and arr2, based on the values returned by the mapping function.

Examples

unionBy([{ id: 1 }, { id: 2 }], [{ id: 2 }, { id: 3 }], x => x.id);
// Returns [{ id: 1 }, { id: 2 }, { id: 3 }]