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Nowadays, users expect sleek, performant web applications that behave more and more like native apps. Techniques have been devised to decrease the waiting time for a website to load on a user’s first visit. However, in web applications that expose a lot of interactivity, the time elapsing between a user action taking place and the app’s response is also important. Native apps feel snappy, and web apps are expected to behave the same, even on less than ideal internet connections.
In this article, I’m going to talk about what React is good at and what makes it work, which should provide you with some context to help you decide if this library could be a good fit for your next project.
What Is React?
React is a Facebook creation which simply labels itself as being
It’s an open-source project which, to date, has raked in over 74,000 stars on GitHub.
- Declarative: you only need to design simple views for each state in your application, and React will efficiently update and render just the right components when your data changes.
- Component-based: you create your React-powered apps by assembling a number of encapsulated components, each managing its own state.
- Learn Once, Write Anywhere: React is not a full-blown framework; it’s just a library for rendering views.
How Does the Virtual DOM Work?
The Virtual DOM is at the core of what makes React fast at rendering user interface elements and their changes. Let’s look closer into its mechanism.
The HTML Document Object Model or DOM is a
programming interface for HTML and XML documents. … The DOM provides a representation of the document as a structured group of nodes and objects that have properties and methods. Essentially, it connects web pages to scripts or programming languages. — MDN
Whenever you want to change any part of a web page programmatically, you need to modify the DOM. Depending on the complexity and size of the document, traversing the DOM and updating it could take longer than users might be prepared to accept, especially if you take into account the work browsers need to do when something in the DOM changes. In fact, every time the DOM gets updated, browsers need to recalculate the CSS and carry out layout and repaint operations on the web page.
React enables developers to make changes to the web page without having to deal directly with the DOM. This is done via the Virtual DOM.
The Virtual DOM is a lightweight, abstract model of the DOM. React uses the
render method to create a node tree from React components and updates this tree in response to changes in the data model resulting from actions.
Each time there are changes to the underlying data in a React app, React creates a new Virtual DOM representation of the user interface.
Updating UI Changes with the Virtual DOM
When it comes to updating the browser’s DOM, React roughly follows the steps below:
- Whenever something changes, React re-renders the entire UI in a Virtual DOM representation.
- React then calculates the difference between the previous Virtual DOM representation and the new one.
- Finally, React patches up the real DOM with what has actually changed. If nothing has changed, React won’t be dealing with the HTML DOM at all.
One would think that such a process, which involves keeping two representations of the Virtual DOM in memory and comparing them, could be slower than dealing directly with the actual DOM. This is where efficient diff algorithms, batching DOM read/write operations, and limiting DOM changes to the bare minimum necessary, make using React and its Virtual DOM a great choice for building performant apps.
Is React Good for Every Project?
As the name itself suggests, React is great at making super reactive user interfaces — that is, UIs that are very quick at responding to events and consequent data changes. This comment about the name React made by Jordan Walke, engineer at Facebook, is illuminating:
This API reacts to any state or property changes, and works with data of any form (as deeply structured as the graph itself) so I think the name is fitting. — Vjeux, “Our First 50,000 Stars“
Although some would argue that all projects need React, I think it’s uncontroversial to say that React would be a great fit for web apps where you need to keep a complex, interactive UI in sync with frequent changes in the underlying data model.
React is designed to deal with stateful components in an efficient way (which doesn’t mean devs don’t need to optimize their code). So projects that would benefit from this capability can be considered good candidates for React.
Chris Coyier outlines the following, interrelated situations when reaching for React makes sense, which I tend to go along with:
- Lots of state management and DOM manipulation. That is, enabling and disabling buttons, making links active, changing input values, closing and expanding menus, etc. In this kind of project, React makes managing stateful components faster and easier. As Michael Jackson, co-author of React Router, aptly put it in a Tweet:
Point is, React takes care of the hard part of figuring out what changes actually need to happen to the DOM, not me. That’s *invaluable*
- Fighting spaghetti. Keeping track of complex state by directly modifying the DOM could lead to spaghetti code, at least if extra attention isn’t paid to code organization and structure.
If you’re curious about how React and its Virtual DOM work, here’s where you can learn more:
- React Videos from Facebook Engineers
- “The Real Benefits of the Virtual DOM in React.js“, by Chris Minnick
- “The difference between Virtual DOM and DOM“, by Bartosz Krajka
- “React is Slow, React is Fast: Optimizing React Apps in Practice“, by François Zaninotto
- “How to Choose the Right Front-end Framework for Your Company“, by Chris Lienert
This is the direction towards which modern web development is heading. It’s not by chance that the latest update of Create React App, a project that makes possible the creation of React apps with zero configuration, has shipped with the functionality of creating progressive web apps (PWAs) by default. These are apps that leverage service workers and offline-first caching to minimize latency and make web apps work offline.
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