LeetCode: Missing Number Solution

1/**
2 * @param {number[]} nums
3 * @return {number}
4 */
5var missingNumber = function (nums) {
6  const n = Math.max.apply(null, [...nums, nums.length])
7  const currentSum = nums.reduce((acc, el) => acc + el, 0)
8  const expectedSum = (n * (n + 1)) / 2
9  return expectedSum - currentSum
10}