Merge 2 sorted arrays without using Extra space in javscript code example

Example: In-place merge two sorted arrays

def merge(X, Y):
 
    m = len(X)
    n = len(Y)
 
    # Consider each element `X[i]` of list `X[]` and ignore the element if it is
    # already in the correct order; otherwise, swap it with the next smaller
    # element, which happens to be the first element of `Y[]`.
    for i in range(m):
 
        # compare the current element of `X[]` with the first element of `Y[]`
        if X[i] > Y[0]:
 
            # swap `X[i] with `Y[0]`
            temp = X[i]
            X[i] = Y[0]
            Y[0] = temp
 
            first = Y[0]
 
            # move `Y[0]` to its correct position to maintain the sorted
            # order of `Y[]`. Note: `Y[1…n-1]` is already sorted
            k = 1
            while k < n and Y[k] < first:
                Y[k - 1] = Y[k]
                k = k + 1
 
            Y[k - 1] = first