What is preact?

Preact is a tiny, fast JavaScript library for building user interfaces, especially web pages. It works a lot like React-another popular UI library-but it’s much smaller (about 3 KB gzipped) and focuses on speed and simplicity. You write components (reusable pieces of UI) in JavaScript, and Preact turns them into HTML that the browser can display.

Let's break it down

  • Components: Small, self‑contained pieces of UI (like a button, a form, or a whole page) written as functions or classes.
  • JSX: A syntax that looks like HTML inside JavaScript, making it easy to describe what the UI should look like. Preact can use JSX, but you can also write plain JavaScript if you prefer.
  • Virtual DOM: Preact keeps a lightweight copy of the page’s structure in memory. When data changes, it updates only the parts of the real DOM that actually need to change, which makes the UI fast.
  • Hooks: Modern Preact provides “hooks” (like useState and useEffect) that let you add state and side‑effects to functional components without writing classes.

Why does it matter?

  • Performance: Because it’s tiny and optimized, pages load faster and feel more responsive, especially on mobile or slow connections.
  • Ease of migration: If you already know React, you can pick up Preact quickly; most React code works in Preact with little or no changes.
  • Lower bandwidth: Smaller bundle size means less data for users to download, which can improve SEO and reduce hosting costs.
  • Community support: Preact has a solid ecosystem, plugins, and a helpful community, making it a viable alternative to larger frameworks.

Where is it used?

  • Single‑page applications (SPAs) that need to be lightweight, such as dashboards, marketing sites, or internal tools.
  • Progressive Web Apps (PWAs) where fast load times are critical.
  • Embedding widgets into existing sites where you don’t want to add a heavy library.
  • Companies like Netflix, Uber, and GitHub have used Preact for parts of their front‑end, and many open‑source projects (e.g., preact-cli, preact-router) are built around it.

Good things about it

  • Extremely small bundle size (≈3 KB gzipped).
  • Near‑identical API to React, making learning and migration easy.
  • Fast rendering thanks to an efficient virtual DOM implementation.
  • Supports modern React features like hooks, context, and fragments.
  • Good TypeScript support and a growing plugin ecosystem.
  • Works well with existing build tools (Webpack, Vite, etc.).

Not-so-good things

  • Some very large React libraries may rely on internals that aren’t fully compatible with Preact, requiring adapters or workarounds.
  • The community, while active, is smaller than React’s, so you might find fewer tutorials or third‑party components.
  • Certain advanced performance optimizations (like concurrent mode) are not yet available.
  • Because it’s less widely adopted, hiring developers with deep Preact experience can be harder than finding React developers.