React
beginnerDefinition
A popular library (a ready-made set of code) written in JavaScript for building the screens of websites and apps out of reusable components.
In the wild
A pizza shop's ordering site is built with React: the menu, the cart, and the checkout button are each a component that updates as customers add pizzas.
More from Websites & Apps
Browser Console
A panel in a web browser's built-in developer tools that shows error messages and notes from a page's code and lets you type commands.
Bundle
The few compact files a website's code is packed into before it goes online, so the browser can download it quickly instead of fetching hundreds of separate files.
Component
A reusable building block of an app's screen, such as a button or a product card, that is built once and placed wherever it's needed.
Context
A React feature that lets one piece of shared information, such as the signed-in user or the dark-mode setting, reach every component that needs it without being handed down layer by layer.
Controlled Component
A form field, such as a text box or checkbox, whose current value is kept in the app's state (the information the app remembers while it runs) instead of being left to the browser, so the app always knows exactly what has been typed.
CSR (Client-Side Rendering)
Building a web page on the visitor's own device: the browser downloads a mostly empty page plus code, then runs that code to draw what you see. The first load can be slow, but moving around afterward is quick.