function max() {
    if(arguments[0].length === 0) {return arguments[1] || NaN;}
    else {
        return max(arguments[0], Math.max(arguments[1] || 0, Math.max.apply(Math, arguments[0].pop())));
    }
};

var a = [[1,2,3],[4,5,6]];

console.log(a);
console.log(max(a));