I want to display the product browsing history, so I am storing the product ids in a browser cookie.
Because the list of history is limited to 5 items, I convert the
You need to actually use the shortened array after you remove items from it. You are ignoring the shortened array.
You convert the cookie into an array. You reduce the length of the array and then you never use that shortened array. Instead, you just use the old cookie (the unshortened one).
You should convert the shortened array back to a string with .join(",") and then use it for the new cookie instead of using old_cookie which is not shortened.
You may also not be using .splice() correctly, but I don't know exactly what your objective is for shortening the array. You can read about the exact function of .splice() here.