Let’s architect a React application from the ground up, exploring the domain and its services, store, application services and the view. The four layers of single page applications — by Alberto V Every successful project needs a clear architecture, which is understood by all team members. Imagine you’re new to the team. The technical leader presents the proposed architecture for the new application coming up on the roadmap: The four layers of single page applications (detailed) He talks about the requirements: Our app will display a list of articles. As a user, I will be able to create, delete and like articles. And then he asks you to do it! Ok, no problem, let’s start architecting I’ve chosen and for type checking. For brevity, the application has no styling. Create React App Flow As a prerequisite, let’s talk about the declarative nature of modern frameworks, touching on the concept of state. Today’s frameworks are declarative React, Angular, Vue are , encouraging us to use elements of functional programming. declarative Have you ever seen a flip book? A flip book or flick book is a book with a series of pictures that vary gradually from one page to the next, so that when the pages are turned rapidly, the pictures appear to animate … [1] Now let’s check a part of React’s definition: Design simple views for each state in your application, and React will efficiently update and render just the right components when your data changes … [2] And a part of Angular’s: Build features quickly with simple, declarative templates. Extend the template language with your own components … [3] Sounds familiar? Frameworks help us build apps consisting of views. Views are representations of state. But what is the state? The state The state represents every piece of data that changes in an application. You visit an URL, that’s state, make an Ajax call to retrieve a list of movies, that’s state again, you persist info to local storage, ditto, state. The state will consist of . immutable objects has many benefits, one being at the view level. Immutable architecture Here is a quote from React’s guide to : optimizing performance Immutability makes tracking changes cheap. A change will always result in a new object so we only need to check if the reference to the object has changed. [4] The domain layer The domain describes the state and holds the business logic. It represents the core of our application and should be agnostic to the view layer. Angular, React, Vue, it shouldn’t matter, we should be able to use our domain regardless of the framework we choose. The domain layer Because we are dealing with immutable architecture, our domain layer will consist of entities and domain services. Controversial in OOP, especially in large-scale applications, the anemic domain model is perfectly acceptable when working with immutable data. For me, this by Vladimir Khorikov was eye-opening. course Having to display a list of articles, the first thing we’ll model is the entity. Article All future objects of type are meant to be immutable. Flow can by making every property read-only (see the plus sign before each prop). Article enforce immutability Now let’s create the using the factory function pattern. articleService Check out this by @mpjme for a great explanation**.** video Since we need only one in our application, we will export it as a singleton. articleService The method will allow us to create of type . Each new article will have a unique autogenerated id and zero likes, letting us supply only the author and title. createArticle frozen objects Article The method freezes an object: that is, prevents new properties from being added to it. [5] **Object.freeze()** The method returns a “maybe” type. createArticle Article types enforce you to check if an object exists before operating on it. Maybe Article If any of the fields necessary to create an article fail validation, the method returns null. Some may argue that it’s better to throw a user-defined exception. If we enforce this and the upper layers do not implement catch blocks, the program will terminate at runtime. createArticle The method will help us update the number of likes from an existing article, by returning a copy of it with the new count. updateLikes Finally, the and methods prevent the from working with corrupt data. isTitleValid isAuthorValid createArticle Validations are very important in keeping our data consistent, especially at the domain level. We can compose our service out of pure functions. Validators Please take these validations with a grain of salt, just for demo purposes. In JavaScript, checking if an object is, in fact, an object is not that easy. :) We now have our domain layer setup! The nice part is that we can use our code right now, agnostic of a framework. Let’s see how we can use the to create an article about one of my favorite books and update its number of likes. articleService The store layer The data which results from creating and updating articles represents our application’s state. We need a place to hold that data, the store being the perfect candidate for the job. The store layer The state can easily be modeled by an array of articles. The implements the publish-subscribe pattern and exports the as a singleton. ArticleStoreFactory articleStore The store holds the articles and performs the add, remove and update immutable operations on them. Keep in mind that the store only operates on articles. Only the , can create or update them. articleService Interested parties can subscribe and unsubscribe to the . articleStore The keeps a list in memory of all subscribers and notifies them of each change. articleStore Our store implementation makes sense for demo purposes, allowing us to understand the concepts behind it. In real life, I recommend using a state management system like , , or at least . Redux ngrx MobX observable data services Ok, right now we have the domain and store layers setup. Let’s create two articles and two subscribers to the store and observe how the subscribers get notified of changes. Application services This layer is useful for doing all kinds of operations which are adjacent to the state flow like Ajax calls to retrieve data from the server or state projections. The application services layer For whatever reason, a designer comes and demands all author names to be uppercase. We know this request is kind of silly and we don’t want to pollute our model with it. We create the to handle this feature. The service will take a piece of state, the author’s name, and project it, returning the uppercase version of it to the caller. ArticleUiService Let’s see a demo on how to consume this service! The view layer Right now we have a fully working application, agnostic of any framework, ready to be put to life by React. The view layer is composed of presentational and container components. Presentational components are concerned with how things look while container components are concerned with how things work. For a detailed explanation check out Dan Abramov’s . article The view layer Let’s build the component, consisting of the and App ArticleFormContainer ArticleListContainer. Now let’s create the React, Angular, it does not matter, forms are complicated. ArticleFormContainer. Check out the library and how it’s methods enhance the declarative nature of our code. Ramda The form takes user input and passes it to the . The service creates an from that input and adds it to the for interested components to consume it. All this logic resides primarily in the method. articleService Article ArticleStore submitForm Notice that the returns the actual form which the user sees, the presentational . This component displays the data passed by the container and emits events like , , and . ArticleFormContainer ArticleFormComponent changeArticleTitle changeArticleAuthor submitForm Now that we have a form to create articles, it’s time to list them. subscribes to the , gets all the articles and displays the . ArticleListContainer ArticleStore ArticleListComponent The is a presentational component. It receives the articles through props and renders components. ArticleListComponent ArticleContainer The passes the article data to the presentational . It also implements the and methods. ArticleContainer ArticleComponent likeArticle removeArticle The method updates the number of likes, by replacing the existing article inside the store with an updated copy. likeArticle The method deletes the article from the store. removeArticle The passes the article data to the which displays it. It also informs the container component when the like or delete buttons are clicked, by executing the appropriate callbacks. ArticleContainer ArticleComponent Remember the crazy request that the author name should be uppercase? The uses the from the application layer to project a piece of state from its original value (string with no rule for uppercase) to the desired one, uppercase string. ArticleComponent ArticleUiService Good work! We now have a fully functional React app and a robust, clear defined architecture. Anyone who joins our team can read this article and feel comfortable to continue our work. :) You can check out the finished app and the GitHub repository . here here If you liked this guide, please clap for it. If you want to help me improve it, I am interested in your comment. @danielDughy [1] [2] [3] [4] [5] https://en.wikipedia.org/wiki/Flip_book https://reactjs.org https://angular.io https://reactjs.org/docs/optimizing-performance.html https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/freeze

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