JS How can I increase the performance of this Max/Min coding challenge?

I’m trying to solve some ‘hackerrank.com’ coding challenges. I’m stuck on this one:

You will be given an array of integers arr and a single integer k. You must create an array arr' of length k from elements of arr such that its unfairness is minimized. Unfairness is defined as max(arr') - min(arr') The function should return the minimum possible unfairness

My code works fine for the majority of test cases. However, in three of those test cases – the ones where the size of arr and k is particularly huge – fail due to an excession of the given time limit.

How can I optimize the performance of my code? Thanks in advance

function maxMin(k, arr) {
    // create array to push unfairness values to
    var unfairnesses = [];
    // sort given array in ascending order
    arr.sort(function(a, b) {
        return a - b;
    });
    // loop over sorted array    
    for(var i = 0; i < arr.length - k + 1; i++) {
        // get array with the length of k at position i
        var tempArr = arr.slice(i, i + k);
        // determine Max and Min of the sliced array
        var tempArrMax = Math.max(...tempArr);
        var tempArrMin = Math.min(...tempArr);
        // get unfairness of the sliced array
        var thisUnfairness = tempArrMax - tempArrMin;
        // push sliced-array-unfairness to unfairnesses array
        unfairnesses.push(thisUnfairness);
    }

    // return minimal value of unfairnesses array
    return Math.min(...unfairnesses);
}

Answer

The two first steps could be:

Your array is sorted. Thus there’s no need to use Math.max and Math.min – the first element of a slice is the smallest, the last is the largest.
When you eliminate Math.max and Math.min calls, you can remove Array.prototype.slice call. Then you’re left with a sort and a single pass over the array.

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Answer