Asynchronous and Synchronous JavaScript. There and back again

Callbacks… Callbacks everywhere… Callback inside the callback, and one more inside! Asynchronous JavaScript code is a pain. Event loop is a JavaScript “bigfoot” – everyone heard about it, almost nobody knows how it works… There is multiple ways you can deal with the asynchronous action: callbacks, Promises, Observables, async-await; but which one is best? Which one should you choose for the particular scenarios?