This section provides an overview of what rxjs is, and why a developer might want to use it.

It should also mention any large subjects within rxjs, and link out to the related topics. Since the Documentation for rxjs is new, you may need to create initial versions of those related topics.

map and select are aliases.

They produce an observable sequence emitting one element every time the source observable emits an element.

If selector is not a function, its value is emitted for each source element.

If selector is a function, the emitted element is the result of running selector on the source element, and can possibly use its position.