In the previous two installments (one, two) we explored the use of callbacks through creating a mapp function for arrays (so called because the latest JavaScripts have a native map method already), and through creating a mapAsync function where the work is done asynchronously rather than serially. The reason for this was so that we could avoid triggering the browser’s “script running a long time” warning and, also, more importantly, provide the user with a responsive UI. […]