How does Ajax handle error management and fallback strategies for when requests fail or when a user has disabled JavaScript in their browser?

For the Ajax way, how is it updating the like count in the database? In the graph it falls under app.post handler, but I didn't see any code for updating.

I am little confused about app.post('/likeAjax/:tt' calling likeMovie(tt) and likeMovie(tt) posting to likeAjax/tt. Are they using each other at the same time? How does that work?

For jQuery methods with the datatype parameter, if we specify a type and the response doesn't match the specified type, what happens?

We can't flash messages in Ajax because rendering does not occur. Is it possible to use 'res.send' to get messages to the browser?

I think going over the concept of Ajax in class will help marinate the concepts into my smooth brain.