What is RxJS?

RxJS is short for Reactive Extensions for JavaScript. Reactive extensions were originally developed by Microsoft as Rx.NET. Since that time, the Reactive extensions library has been implemented for several other languages, including Java, Python, Ruby and JavaScript. But that doesn’t really answer the question.

What is RxJS? According to the documentation, “RxJS is a library for composing asynchronous and event-based programs by using observable sequences.”

What does that mean? Think of RxJS as a way to manage data as it flows through time, similar to how Apple’s flow on a conveyor belt. First we collect. Apples are picked, hauled and loaded onto a conveyor, creating a stream of apples. Similarly, we use RxJS to send an HTTP request and receive the response, creating a stream of data. The stream is observable. We can watch it as items are added or emitted to the stream. We pipe the stream of apples through a set of operations. As each apple flows through, we transform the apple by cleaning it, filter it by quality or size, and process it of fixing a label, for example. Likewise, we pipe our data through a set of operations to transform, filter or process our data. Using query like operators, we combine streams to merge their results. In our apple example, we combine the green apple stream with a red apple stream to create a mixed bag of apples. Correspondingly, we combined a stream of customer data with the stream of invoice data to display a customer with their overdue invoices, and we can cache the stream. This one doesn’t fit as well into our apple metaphor. But when working with data, we may want to cache it in a service to reuse the data without another HTTP request.

Going back to the definition, we restate this as “RxJS is a library for composing observable streams and optionally processing each item in the stream using an extensive set of operators.” RxJS helps us better manage and manipulate the data needed in our application. There are other techniques for  managing asynchronous and event-based data.

A callback is a function that can be called back after an async operation is complete, but callbacks can be difficult to manage when working with nested async operations.

A promise is an object that may produce a single value sometime in the future. It can only handle a single emission and is not cancelable.

async/await is a special syntax that allows writing asynchronous code that looks synchronous. It also can only handle a single emission and is not cancelable.

Why use RxJS and not one of these approaches? Using RxJS has several advantages. RxJS provides a single technique for working with any type of data. We often work with multiple sources of data. Events from the keyboard, mouseover routes and data from various files, databases or third party APIs. With RxJS, we work with different data sources using the same techniques and operators. Our views often require data combined from several sources. We easily compose data with RxJS. RxJS can produce multiple values over time and uses a push model to notify our code when specific actions occur, making it easy for us to watch and react to user interactions or data changes. RxJS is lazy. Evaluation does not start until subscription. So we can create recipes that only execute when we need the result. For the best user experience we want to handle errors gracefully. RxJS has built-in error handling and with RxJS we can cancel asynchronous actions. For example, if a user clicks on Product A and then quickly clicks on Product B, we can cancel the request for Product A and only return Product B.

So many great advantages to RxJS that Angular built it in into several key features. For example, Angular uses RxJS in routing to watch for changes to route parameters, route data or router events. In Reactive Forms to watch for value changes as the user modifies input elements on a form and when communicating with the backend server, sending requests and receiving responses using HTTP client. That’s why Angular installs RxJS as part of its core set of libraries. We can expand our use of RxJS in our Angular applications to move towards more Reactive Development.

What is Reactive Development?

From Wikipedia, Reactive Development, also called Reactive Programming, is a declarative programming paradigm concerned with data streams and the propagation of change. As the user makes a selection, data is retrieved from a backend server or some other system status changed. That change is propagated and the application reacts appropriately updating the display or performing another action. In addition, reactive development is functional.

“The essence of functional reactive programming is to specify the dynamic behavior of a value completely completely at the time of declaration.” – Heinrich Apfelmus.

Reactive Development

A reactive system is quick to react to user interactions, resilient to failure with good error handling and reactive to state changes, meaning the code watches for change events and reacts, instead of procedurally calling methods.

What is the Web Animations API?

In the context of web apps, animation is nothing more than the visualization of change over a specified duration. This visualization of change is very important because when done right we can use this to dramatically increase the user experience of an app and make our apps feel more refined and well designed.

At the highest level, the Web Animations API is a standardized JavaScript API which is baked into browsers that allows developers to animate DOM elements. CSS was always been the most performant way to animate on the web because the CSS animations engine can run animations on the GPU instead of the CPU allowing us to achieve smooth 60 fps animations. The Web Animations API finally allows us to write animation logic using JavaScript and opens up the browsers animation engine allowing us to run these animations on the GPU. As well as performant animations there are host of other benefits the Web Animations API provides us. Because it is a JavaScript API we can easily create dynamic animations by altering durations, easing methods and other variables; something which is very hard to do in CSS. The API provides very flexible playback control which allows us to Pause, Rewind, Skip and even change the rate of playback and more. The API is Promise based so it is really easy to chain multiple animations or run other logic when the animation completes. And because the Web Animations API is a browser feature there are no external dependencies to manage or maintain. Today most JavaScript libraries take a component based approach. Whether that’s using Angular, React, VueJS or just native web components the Web Animations API fits in with this architecture because the JavaScript used to create this animations can be embedded into the components easily without any dependencies. These are great benefits provided by the Web Animations API which we can use to harness the power of the GPU to create silky smooth animations that are dynamic and flexible.


ActiveRecord is a component of Rails that makes it extremely efficient to build and manage your data. Each ActiveRecord Model represents a table in the database. A row is created in the database when an instance of a model is created and saved.