如何将回调传递给我传递给“vo”库的生成器？

I am trying to understand how callbacks work so I created a function and passed a second argument named 'callback', which I call at the end of the function with 'callback(arr)' . However I am getting an error which says : "callback is not a function" ? Can you please tell me what I am doing wrong?I am trying to understand how callbacks work so