A JavaScript library for building fast, declarative user interfaces.
React (or ReactJS) is an open-source **front-end JavaScript library** developed by Meta. Its primary goal is to help developers efficiently build complex, interactive user interfaces. It's not a full framework (like Angular), but rather a tool focused specifically on the "View" layer of an application, making it highly flexible and composable.
React encourages building encapsulated pieces of UI, known as **components**. Think of them as
custom, reusable HTML elements (like a `
Instead of telling the browser *how* to update the DOM (imperative), you tell React *what* the final UI should look like for a given piece of data. React then takes care of the efficient updates. This makes your code more predictable and easier to reason about.
React keeps a lightweight copy of the real DOM in memory (the VDOM). When data changes, it compares the current VDOM to the new state (diffing) and only updates the *specific* parts of the real HTML that have changed. This leads to massive performance gains.
JSX is a syntax extension that allows you to write HTML-like markup directly inside your JavaScript files. It combines logic and markup, making component code highly cohesive and readable. It gets transpiled into regular JavaScript before the browser runs it.