I have been toying with the idea of creating a simple extendable pagination service for angular using RxJs.

RxJS (Reactive Extensions for JavaScript) is a powerful library for reactive programming in JavaScript. It provides a set of tools and operators that enable developers to work with asynchronous and event-driven code in a more functional and declarative manner. RxJS is heavily based on the concept of Observables, which are streams of data that can be observed and manipulated over time.

Reactive programming, as facilitated by RxJS, allows you to work with data streams and events in a consistent and composable way, making it easier to handle complex asynchronous scenarios. It's particularly useful for scenarios like handling user input, managing AJAX requests, working with real-time data, and managing state changes in web applications.

Key concepts and features of RxJS include:

1. Observables: Observables represent sequences of data over time. They can emit values, errors, and completion signals. Observables can be subscribed to, and you can perform operations on them using various operators.

2. Operators: Operators are functions provided by RxJS that allow you to transform, filter, combine, and manipulate data streams. Operators enable you to compose complex asynchronous logic in a concise and readable manner.

3. Subscription: Subscribing to an Observable allows you to receive values and notifications emitted by the Observable. Subscriptions can be managed to control when data is consumed and to avoid memory leaks.

4. Subjects: Subjects are a type of Observable that allows you to both emit values and subscribe to them. They are often used for creating event emitters or managing state changes.

5. Schedulers: Schedulers provide a way to control the execution context and timing of Observables. They are useful for managing concurrency and handling asynchronous operations on different threads or environments.

6. Error Handling: RxJS provides mechanisms for handling errors and recovering from them within data streams.

7. Hot and Cold Observables: Observables can be categorized as "hot" or "cold" based on when they start emitting data. Hot Observables emit data regardless of whether there are subscribers, while cold Observables start emitting data only when a subscriber is present.

RxJS is widely used in modern JavaScript and web development, especially in frameworks like Angular, where it's used for handling asynchronous operations, managing state in applications, and implementing features like data fetching, debouncing, and more. While RxJS can have a learning curve, mastering its concepts can lead to more efficient and maintainable asynchronous code.