Mastering JavaScript Functional Programming - Second Edition

Observer and reactive programming

The idea of the observer pattern is to define a link between entities, so when one changes, all of the dependent entities are updated automatically. The observable can publish changes to its state, and its observer (which subscribed to the observable) will be notified of such changes. 

There is a proposal for adding observables to JavaScript (see https://github.com/tc39/proposal-observable) but as of December 2019, it's still stuck at stage 1; check https://github.com/tc39/proposal-observable/issues/191. Hence, for the time being, it seems that using a library will still be mandatory.

There's an extension to this concept called reactive programming, which involves asynchronous streams of events (such as mouse ...