1
var subsetXORSum = function (nums) {
2
  let output = [];
3
  backtrack();
4
  return output.reduce((a, b) => a + b);
5
  function backtrack(start = 0, arr = [nums[0]]) {
6
    output.push([...arr].reduce((a, b) => a ^ b, 0));
7
    for (let i = start; i < nums.length; i++) {
8
      arr.push(nums[i]);
9
      backtrack(i + 1, arr);
10
      arr.pop();
11
    }
12
  }
13
};