Learn about RxJS to write efficient asynchronous code. Explore subjects, operators, and observables. Gain insights into creating projects like a reactive local database and handling DOM events.

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RxJS (Reactive Extensions for JavaScript) is a very powerful library for web development which allows you to easily write asynchronous or call-back code.

In this course, you will explore the latest version of RxJS in detail, focusing on how to apply the reactive paradigm to solve your day-to-day tasks. You will learn all the major components of this library including: subjects, operators, and how to test observables.

In the last section of this course, you will get hands-on with this library to create your own project. Throughout this project, you’ll learn about building a centralized loading indicator, how to handle DOM events, how to build a reactive local database, and more.

By the end of this course, you will have a great new skill to add to your resume, and a cool new project for your portfolio.

Building Reactive Applications with RxJS

In the previous sections, you were introduced to the world of reactive programming, and you were able to see how Observables can ease your programming life. You were also introduced to the concept of a **data pipeline**, where all the fun happens, and you learned how several sequential operations is applied to the data passing through the pipeline in order to transform it and adapt it to Observer needs.

# What are operators

An **operator** is a **pure function** that can be applied to the data flowing in the pipeline at any point. By **pure function**, we mean that it doesn't change any external state, and it doesn't change the Observable that pushed the value into the pipeline where this function operates. Instead, it produces a new Observable that will flow down the pipeline.

# Operator categories

In this section, you will be introduced to the most common RxJS operators that make data transformation seamless. We have organized these operators in different categories based on their functionality:



1. **Creation operators**

2. **Combination operators**

3. **Filtering operators**

4. **Transformation operators**


Once you get familiar with some **operators** from each category, you will be able to build powerful data pipelines to tackle different problems.

At the end of this chapter, you will be able to make your own custom **operator** and understand the inner working of each **operator** out there.

Let's get our hands dirty!

Get introduced to the operators and their types in RxJS.

The Need for Reactive Programming

RxJS Subjects

RxJS Operators

Testing Observables

Real-World Projects in RxJS

Conclusion

Overview of Operators in RxJS