Nested arrays suming integers

function arraySum(arr) {
    var sum, i, j, cur;

    sum = 0;

    for (i = 0, j = arr.length; i < j; i++) {
        cur = arr[i];

        if (cur instanceof Array) {
            sum += arraySum(cur);
        } else if (typeof cur === "number") {
            sum += cur;
        }
    }

    return sum;
}

console.log(arraySum([[1,2,false],'4','5']));    // 3
console.log(arraySum([[1,2,3],4,5]));            // 15
console.log(arraySum([[[[[[[[[1]]]]]]]], 1]));    // 2