What is React?
React is a JavaScript library for building user interfaces out of reusable components that declaratively describe what the UI should look like for a given state. It uses a virtual DOM to compute the minimal set of real DOM updates needed when state changes, rather than manually mutating the page.
Example
function Greeting({ name }) { return <h1>Hello, {name}</h1>; } is a React component.
Related tool
Try it on ToolSphere — runs entirely in your browser, nothing is uploaded to a server.