intersectionBy

Returns a list of elements that exist in both arrays, after applying the provided function to each array element of both.

Create a Set by applying fn to all elements in b, then use Array.prototype.filter() on a to only keep elements, which produce values contained in b when fn is applied to them.

typescript

export type MapFunc<T = any> = (val: T, index?: number, arr?: T[]) => T;
const intersectionBy = (a: any[], b: any[], fn: MapFunc) => {
  const s = new Set(b.map(fn));
  return [...new Set(a)].filter((x) => s.has(fn(x)));
};

typescript

intersectionBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [2.1]