What React does
React is a JavaScript library that builds user interfaces. A user interface is everything you see and interact with on a website: buttons, forms, navigation menus, product cards, shopping carts. React gives developers a structured way to create these elements and make them interactive.
Without a tool like React, building a complex website means writing thousands of lines of code to manually update what the user sees whenever data changes. React automates that. You tell it what the interface should look like given certain data, and React figures out how to update the screen efficiently.
Components: the building blocks
React is built around the concept of components. A component is a self-contained piece of the interface. A navigation bar is one component. A product card is another. A checkout form is another. Each component manages its own appearance and behavior.
Components are reusable. Once you build a product card component, you can use it on the homepage, the search results page, and the category page. Change the component once and it updates everywhere. This is why React scales well for large applications.
The virtual DOM
The DOM (Document Object Model) is the browser's internal representation of a web page. Updating the DOM directly is slow. React solves this with a virtual DOM, which is a lightweight copy of the real DOM that exists in memory.
When something changes, React updates the virtual DOM first, compares it to the previous version, and then updates only the specific parts of the real DOM that changed. This diffing process makes React fast even for complex interfaces with hundreds of interactive elements.
Why React became dominant
- Facebook built and maintained it, giving it credibility and resources
- The component model matched how designers think about interfaces
- A massive ecosystem of third-party libraries solved common problems
- React Native extended the same concepts to mobile app development
- The job market created a self-reinforcing cycle: more developers learned React because companies used it, and companies used it because developers knew it
React vs Vue vs Angular
Vue.js is simpler to learn and has an elegant API. It is popular in Asia and among smaller teams. Angular is a full framework (not just a UI library) backed by Google. It includes routing, forms, HTTP requests, and more out of the box. Angular is common in large enterprise applications.
React sits in the middle. It is a library (you choose your own tools for routing and state management) with the largest community and ecosystem. For most new web projects in 2026, React is the default choice.
CodePup AI generates React code because it has the widest ecosystem, the most available developers, and works well with modern tools like Next.js and Tailwind CSS.
React and Next.js
React by itself only handles the user interface. Next.js is a framework built on top of React that adds server-side rendering, routing, image optimization, and deployment tools. Most production React applications in 2026 use Next.js rather than React alone.
Do you need to know React?
If you are using an AI builder like CodePup AI, you do not need to know React. The AI generates the React code for you. But understanding what React is helps you evaluate the output, communicate with developers, and make better decisions about your product's technical direction.