BETTER solution to You Can't JavaScript Under Pressure Question 5

gistfile1.js

function acc(pV, cV) { 
    if (cV instanceof Array) { 
        return pV + cV.reduce(acc, 0); 
    } else if (typeof cV == 'number') { 
        return pV + cV; 
    }
}

function arrSum(i) {
    return i.reduce(acc, 0);
}