A util function like filter that also returns an array that doesn't match

split.ts

type Split<T> = [T[], T[]];
export function split<T>(arr: T[], isMatch: (item: T) => boolean): Split<T> {
    return arr.reduce<Split<T>>((rv: [T[], T[]], item: T) => {
        if (isMatch(item)) {
            rv[0] = [...rv[0], item];
        } else {
            rv[1] = [...rv[1], item];
        }
        return rv;
    }, [[], []] as Split<T>);
}

const [match, noMatch] = split([1,2,3,4,5], (i) => i % 2 === 0);
// match = [2, 4]
// noMatch = [1, 3, 5]