Race two callbacks

race.ts

type Cont = (callback: (a: any) => void) => void;

const timeout500: Cont = (next) => setTimeout(next, 500, 'timeout500');

const timeout1000: Cont = (next) => setTimeout(next, 1000, 'timeout1000');

const race
    : (a: Cont, b: Cont) => Cont
    = (a, b) => (next) => {
        let resolved = false;
        const f = (a) => {
            if (!resolved) {
                resolved = true;
                next(a);
            }
        }
        a(f);
        b(f);
    }

race(timeout500, timeout1000)(console.log);