Create permutations from two or more given list

Permutations.js

/**
 * Create permutations from two or more given list
 * Based on Heap's Algorithm
 */
 function permutations() {
    var r = [], arg = arguments, max = arg.length-1;
    function helper(arr, i) {
        for (var j=0, l=arg[i].length; j<l; j++) {
            var a = arr.slice(0); // clone arr
            a.push(arg[i][j]);
            if (i==max)
                r.push(a);
            else
                helper(a, i+1);
        }
    }
    helper([], 0);
    return r;
}

console.log(permutations(["4",5,"6"], [1,2], [7,8,9]))