const max = (data, key = n => n) =>
Array.prototype.reduce.call(data, (max, n) => {
const val = key(n);
return val > max[1] ? [ n, val ] : max;
}, [ null, -Infinity ]);
const [ item, value ] = max(
form.querySelectorAll('.kursBtn'),
n => +n.nextElementSibling.value
);
form.querySelector('#winner').value = `${item.name} - ${value}`;