Don’t expect a deep dive into all RxJS operators, but rather expect an explanation of how to draw, think, and reason about reactive web applications. The goal of the course is to teach you how to comfortably design and develop applications in Angular in Reactive style using just plain RxJs, and nothing more. When we think about the functionality of our application, we quickly notice that there are quite a few corner cases and special scenarios. In this article, we will explain how to write a reactive calendar application in only a few lines of code (spoiler: It’s gonna be real time too). In this article, I want to talk about practical scenarios that I found useful while working with Angular and RxJS, going through useful patterns you may use and what to look out for. A magical thing about them is that they flatten themselves. You shouldn't see a nested subscription in rxjs. Navigate to previous and next days, weeks, and months. It is used to show the appointments in all the different views, and it is dependent on a bunch of streams: This looks a bit more complex, but let’s give it a go. I logged out the result of a map function that contained asynchronous behaviour in the middle of a stream, and saw this in my console: I expected to see the result of an HTTP request, but instead saw another observable. We use subjects because we need to control the values of the streams ourselves, and we use the BehaviorSubject in particular because all our source streams need an initial value. RxJS is JavaScript library for transforming, composing and querying asynchronous streams of data. We will use Angular, Angular Material, TypeScript, RxJS, Firebase, and AngularFire as our main technology stack. I’ve created the git branch initial to get us started. We can use animationFrame and the interval static method of Observable to create an observable that emits one event every time the browser is ready to display a new frame. Edit the code and find out. Both of these articles are focussing on “trying to make the mind switch towards reactive programming”. Don’t think about who triggers what. Note: We use the async pipe from Angular to subscribe/unsubscribe the streams automatically. First of all, we have to clone the project locally and check out the initial branch. The situation of the problem goes like this: Solution: shareReplay() will emit those values but keep track of them. Dealing with time and coordinating different types of events can be tricky. It's a paradigm shift. RxJS' observables don't do this automatically, but the library provides us with ways to flatten observables when we choose. The first observable emits 3 more observables with different content (letters, numbers, emoji). Just by thinking about source streams and presentational streams, it wasn’t even that hard. Important information you need to know in order to become an effective reactive programmer. Let’s take, Click on the “CREATE PROJECT” button. Like the above example, that results in a nested stream (HTTP response inside a stream of input change events), so the result needs to be flattened to be used easily in the UI. There is only one problem. It might look something like this: Since we are using BehaviorSubjects, the streams will get an initial value (which is what we want, of course). In my previous article I explored the ways in which RxJS makes frontend development in Angular so much more fun and easy than it is; we discussed the topics of reducing the component state, deriving view state from actual state using RxJS operators instead of imperative commands, and thinking in a reactive way in general. The website rxmarbles.com has a great playground for learning how to use and draw marble diagrams. Make sure you have the latest version of this document. These subjects get values from the simple interactions from the template. Let’s not even imagine that we have to combine that with asynchronous actions as well. Because the first async pipe triggered the first emit the rest of the async pipes will miss that value. See the Pen That way, the async pipes will never miss a value. Note: For readability purposes, we will suffix all the streams with a $ symbol. The 3 nested observables have been flattened into one, and all the values have been preserved. We have created it in no time and with only a few lines of code. Below is a code example which the typescript transpiler complains about saying: Error:(131, 21) TS2304:Cannot (used RxJS parts: publishReplay, Subscription) We kept the component untouched and only applied changes to the service. I hope that you have enjoyed this post, if you would like to learn a lot more about RxJs, we recommend checking the RxJs In Practice Course course, where lots of useful patterns and operators are covered in much more detail. switchMap behaves differently. Like I said before, nested streams might work well for processing data, but might not work for displaying data to your end users. If your application converts something into an observable from inside the map operator, the next operator in your pipe will receive an observable, and you'll have a … I started with one Observable that emitted names of files found one folder, but as the program discovered subdirectories, it emitted more Observables which emitted more file names and more Observables. Maybe RxJS it's not more popular than it is because thinking in streams is super-hard. RxJS in Action gives you the development skills you need to create reactive applications with RxJS. RxJS requires a different mode of thinking, but it is very worthwhile to learn and use. a single stream that emits a number once a second, rxjs flatMap vs switchMap in a to-do list, rxjs switchMap vs flatMap in fuzzy search, The myth of AngularJS migration: Moving from JS to Angular 11 is going to feel like replatforming →, Five common myths that will postpone your legacy modernization →, Creating a useful GraphQL server using AWS Amplify →. In the Authentication tab, go to “SIGN-IN METHOD” and enable the “Anonymous” setting. The first time I encountered a higher-order observable was a surprise. I don’t believe that to be the case when writing complex streams. Learn about RxJS 6 and Observables in-depth, and using RxJS to manage common and complex async scenarios within an application. All other incoming events from the first two streams are discarded. While the stream in the previous example emitted 1, 2, 3, 4..., this stream emits new streams. Later, we look at RxJS, as a library and master it. We can complete the Firebase configuration in a few steps: Let’s continue. Streams can be documented by ASCII documentation. Set the read and write property to “true” and click “publish”: Go back to the overview by clicking on the home icon, and then select “Add Firebase to your web app”. I hope that I can encourage more people to take on this reactive approach and start writing kick-ass applications. For every interaction the user makes in the UI, the app needs to handle that specific interaction accordingly. Modify the last line to look like this: When the second stream starts emitting numbers, switchMap only puts the numbers from the second stream into the flattened stream. Working with RxJS is a little bit like having superpowers: your powers allow you to do extraordinary things, but they’re easy to misuse, and when that happens — it can be quite dangerous! Anyone working on an Angular app should at least be familiar with RxJS. Let’s call them presentational streams. The ways higher-order observables are created, How to recognize a higher-order observable when you encounter one, How to visualize their streams of events in RxViz, How to visualize flattening a higher-order observable into a regular (or first-order observable) with. As you can see, this just handles static data, the buttons/inputs won’t work, and the appointments are not loaded yet. Yes, we would have to update a bunch of stuff. So basically, it gives us a function where we have all the information we need. This is the beginning of thinking reactively. RxJS is a library for composing asynchronous and event-based programs by using Copy the config with the correct properties and replace the firebaseConfig object in src/app/app.module.ts with these properties. See the Pen Just like we calculated the currentWeek$ based on the currentDateM$, we can do the same thing here. RxJS in Action gives you the development skills you need to create reactive applications with RxJS. This book is full of theory and practical examples that build on each other and help you begin thinking in … In my first project at Rangle, I jumped into a codebase that used redux observable, a combination of RxJS and Redux for managing state and side effects like calls to our backend & 3rd party APIs. The complete code You will start thinking about your problems in a different way As RxJS continues to evolve, these guidelines will continue to evolve with it. Let’s take this code sample, for instance: I marked the input properties with XX to show what our components need in terms of data. E.g. So in short, it’s not just a date, but a moment wrapper. Promises can be used in long chains or nested deeply within each other, but calling .then on the outermost one will retrieve the value from innermost one when it resolves. See if you can explain why. The share() operator is an alias for publish().refCount() and will share the subscription. Take this crazy (but simple) example, for instance. This book is full of theory and practical examples that build on each other and help you begin thinking in a reactive It contains the default logic/components, setup, and styles. The appointments$ is a stream that will be provided to us by AngularFire, but the viewMode$, searchTerm$, and navigation$ are simple behavior subjects. RxJs provides a Scheduler called animationFrame which wraps the requestAnimationFrame browser API. Since that is not really part of this article, I’m only going to show a small example below. When applied to one observable, it captures all the events emitted by nested observables and moves them up into the first observable's stream. A higher-order observable might be the right way to process or represent data in a computer's memory, but it also might not be the way the way to deliver data to a consumer, such as a UI component or another part of your application. You may type faster than the server can respond to search requests, and we only care about the most recent request's response. You can do this without using the of or from functions directly because libraries you rely on might use them. We use the same observables multiple times in our template. Reactive web applications can be overwhelming in the beginning, but eventually, they can be really rewarding. Thinking in streams So far, we have gone through a bunch of scenarios that have shown us which operators are at our disposal and how they can be chained. This is the most important stream. We thoroughly describe how Redux works and how to implement it from scratch. Kwinten. Click on database and navigate to the rules tab. Thinking in streams. Other RxJS operators were like nothing I had seen before, such as flatMap, and switchMap. In the terminal, we have to go to the folder where we want to install the project and run the following commands: We are using Firebase as our backend because it requires minimal setup, it’s realtime by default, and AngularFire gives us streams for free. Thinking in functional reactive programming can be difficult, but we will give you some fundamentals to go about composing streams. Based on the currentDateM$ we can calculate the current week. Marble diagrams are a great way to do that. The suffix M after the currentDate property shows that the type is Moment. I would like to give special thanks to the awesome people that reviewed this post and gave me pointers: Software architect/trainer/coach/speaker/blogger, Twitter The appointments in Firebase, the view mode, the search term, and the current date. Make sure you have the latest version of this document. Once the code had walked all the way down the tree of files and subdirectories, it returned an Observable with a stream that mirrored the structure of my file system (with Observables in the place of directories), rather than a simple list of files. The complete component looks like the code snippet below now. This article is all about making the paradigm switch from thinking imperatively towards thinking reactively. When the third stream starts emitting emojis, the flattened stream only includes emojis from then on. The goal is to write the reactive part ourselves. We know the presentational streams, which are simply the streams that our components need. RxViz is a fantastic tool that can animate observables emitting streams of events, helping you determine if your code is behaving the way you expected. When I tried out RxJS outside the scope of that project for file system operations and web sockets, I also saw behaviours that I couldn't relate to other things in Javascript, like streams of events coming from streams of events. This course comes with a running Github repository with the the finished code, as well as starting points for different sections of the course in case that you want to code along, which we recommend as its the best way to learn. I found marble diagrams like the ones on https://rxmarbles.com were good for explaining some some stream concepts, but RxViz's animation made the idea of nested streams click in my head. But there is … Let's use this as an example of a higher-order observable in RxViz, Like the last example, this is a higher-order observable. Here are two very common UI elements using streams to manage their (fake) HTTP requests to a server. And often times, they think that hard things will be easy. The two last chapters of the book cover everything NgRx has to offer in terms of core functionality Now we have to think about the data that our components need, because those components will need to be updated based on those source streams. The first presentational stream we need is viewMode$. on CodePen. It was time to step back from my practical projects and explore the concept of nested streams and higher-order observables on its own. That means you outer observable has become a higher-order observable. The share() operator will emit that value on the first subscription. Consider it some homework. The library comes with many operators, which can be used to deal with almost every situation we … Now we should be redirected to. One could argue that code should not be documented and be self-explanatory. The calendar should be completely functional in your browser. Since observables are cold by default, they will get executed every time there is a subscription. 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