asssigned array variable not changed outside of scope [duplicate]

Hi sorry if this questions is terrible. I have been working through leetcode and found what I thought to be unexpected behaviour in javascript.

/**
 * @param {number[]} nums
 * @param {number} k
 * @return {void} Do not return anything, modify nums in-place instead.
 */
var rotate = function(nums, k) {
    var temparr = nums.splice(0,k)
    nums = nums.concat(temparr)
    console.log(nums)
};

Your input
[-1,-100,3,99]
2

stdout
[ 3, 99, -1, -100 ]

Output
[3,99]

>Expected
[3,99,-1,-100]

The variable nums = [ 3, 99, -1, -100 ], however the nums out of scope of the function is equal to [3,99], why does this occour and I making some mistake in scope thanks.