Differences to React

Preact itself is not intended to be a reimplementation of React. There are differences. Many of these differences are trivial, or can be completely removed by using preact-compat, which is an thin layer over Preact that attempts to achieve 100% compatibility with React. The reason Preact does not attempt to include every single feature of React is in order to remain small and focussed - otherwise it would make more sense to simply submit optimizations to the React project, which is already a very complex and well-architected codebase.

What's Included?

• ES6 Class Components
• High-Order Components
  • (components that return other components from render(), effectively wrappers)
• Stateless Pure Functional Components
  • (functions that receive props as arguments and return JSX/VDOM)
• Simple but effective Virtual DOM diffing
• h(), a more generalized version of React.createElement (read: why h()?)

What's Added?

Preact actually adds a few convenient features inspired by work in the React community:

• [Linked State] updates state when inputs change automatically
• Batching of DOM updates, debounced/collated using setTimeout(1) (can also use requestAnimationFrame)
• You can just use class for CSS classes. className is still supported, but class is preferred.
• Setting class to an Object creates a String className containing the keys having truthy values.
• Component and element recycling/pooling.

What's Missing?

• PropTypes: Not everyone uses them, so they aren't part of Preact's core. They are supported in preact-compat.
• [Contexts]: Support for context has been added and will be released in 3.0.
• [ReactChildren]: If you absolutely must use it, use preact-compat.