This code defines two functions: mergeSort and merge. The mergeSort function takes an array as input and sorts it in ascending order using the Merge Sort algorithm. The function starts by checking if the length of the array is 1 or less. If so, it simply returns the array as it is already sorted. Otherwise, it finds the middle index of the array and stores it as the variable middleIndex. It then splits the array into two halves, the leftArr and rightArr, depending on the value of middleIndex. The mergeSort function then calls itself recursively on the leftArr and rightArr, and passes the returned values to the merge function. The merge function takes two input arrays, leftArr and rightArr, and initializes an empty array called sortedArr The function then initializes two variables, i and j, to 0. The function then enters a while loop, which continues to execute while i is less than the length of the leftArr and j is less than the length of the rightArr. In each iteration of the loop, the function compares the ith element of the leftArr and the jth element of the rightArr. If the ith element is less than the jth element, the ith element is added to the bottom of the sortedArr. Otherwise, the jth element is added. The loop iterates until all the elements of leftArr and rightArr have been added to the sortedArr. The sortedArr is then returned, and the mergeSort function returns the result of the merge. In summary, this code implements the Merge Sort algorithm to sort an input array in ascending order by recursively dividing the input array into subarrays, sorting them, and then merging the subarrays back together in sorted order.