fromEvent is a function that accepts a source of events, such as click events on a toggle. As a result, it creates a sequence of events over time. This sequence is called a stream.

Reactive programming is programming with streams.

Reactive stream libraries like RxJS let you:

• create a stream from various sources
• transform and filter a stream in different ways
• combine multiple streams
• and more!

See also

map vs filter

Pipeable operators - Build your own with RxJS!

zip vs combineLatest

The JavaScript pipeline operator proposal