React is the JavaScript library that powers the user interfaces of Facebook, Instagram, Netflix, and millions of other websites. It was created by Facebook, and it changed how developers build websites: instead of writing pages as one big block of HTML, you build them from small, reusable pieces called components. If you know JavaScript and want to build modern, interactive websites, React is the most useful next step you can take.

How does React work? You build your interface from components — a button, a header, a product card — and each component is a JavaScript function that returns what should appear on screen. When your data changes, React updates only the parts of the page that need to change, using its virtual DOM to work out the difference quickly. State holds the data that changes, like what a user typed or which tab is open, and props pass data down from a parent component to its children.…