|Transform function to apply to each source element or an element to yield. If selector is a function, it is called with the following information: 1. the value of the element, 2. the index of the element, 3. the Observable object being subscribed.|
|Object to use as |
select are aliases.
They produce an observable sequence emitting one element every time the source observable emits an element.
selector is not a function, its value is emitted for each source element.
selector is a function, the emitted element is the result of running
selector on the source element, and can possibly use its position.