hackerrank counting valleys problem code example

Example: the hiker first enters a valley 2 units deep

function countingValleys(n, s) {    let level = 0;    let result = 0;    [...s].reduce((target, step) => {        step.match(/u/i) ? level++ : level--;        (!target && level >= 0) && (result++);        target = !!(level >= 0);        return target;    }, true);    return result;}