Find Median of Two Sorted Arrays in JS

The task is taken from leetcode

There are two sorted arrays nums1 and nums2 of size m and n respectively.

Find the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)).

You may assume nums1 and nums2 cannot be both empty.

Example 1:

nums1 = [1, 3]

nums2 = [2]

The median is 2.0

Example 2:

nums1 = [1, 2]

nums2 = [3, 4]

The median is (2 + 3)/2 = 2.5

My solution

/**
 * @param {number[]} nums1
 * @param {number[]} nums2
 * @return {number}
 */
var findMedianSortedArrays = function(nums1, nums2) {
  let i1 = i2 = 0;
  let smallest, valBefore;
  const pivot = Math.floor((nums1.length + nums2.length) / 2);

  while (nums1[i1] || nums2[i2]) {
    smallest = (nums2[i2] === void 0 || nums1[i1] < nums2[i2])
      ? nums1[i1++]
      : nums2[i2++];

    if ((nums1.length + nums2.length) % 2) {
      if (pivot === i1 + i2 - 1) {
        return smallest;
      }
    } else {
      if (pivot - 1 === i1 + i2 - 1) {
        valBefore = smallest
      }
      if (pivot === i1 + i2 - 1) {
        return (smallest + valBefore) / 2;
      } 
    }
  }
};

This is the first idea that I had and it reached 99th percentile. I guess you can't take this evaluation seriously. And I'm sure there's a better solution.