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 a 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 focused - otherwise it would make more sense to simply submit optimizations to the React project, which is already a very complex and well-architected codebase.
Version Compatibility
For both Preact and preact-compat, version compatibility is measured against the current and previous major releases of React. When new features are announced by the React team, they may be added to Preact's core if it makes sense given the Project Goals. This is a fairly democratic process, constantly evolving through discussion and decisions made in the open, using issues and pull requests.
Thus, the website and documentation reflect React
0.14.x
and15.x
when discussing compatibility or making comparisons.
What's Included?
- ES6 Class Components
- classes provide an expressive way to define stateful components
- Higher-Order Components
- components that return other components from
render()
, effectively wrappers
- components that return other components from
- Stateless Pure Functional Components
- functions that receive
props
as arguments and return JSX/VDOM
- functions that receive
- Contexts: Support for the legacy
context API
was added in Preact 3.0.- Support for the new api is discussed as PR #963.
- Refs: Support for function refs was added in Preact in 4.0. String refs are supported in
preact-compat
.- Refs provide a way to refer to rendered elements and child components.
- Virtual DOM Diffing
h()
, a more generalized version ofReact.createElement
- This idea was originally called hyperscript and has value well beyond the React ecosystem, so Preact promotes the original standard. (Read: why `h()`?)
- It's also a little more readable:
h('a', { href:'/' }, h('span', null, 'Home'))
What's Added?
Preact actually adds a few convenient features inspired by work in the React community:
this.props
andthis.state
are passed torender()
for you- You can still reference them manually. This is just cleaner, particularly when destructuring
- 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, butclass
is preferred. - Component and element recycling/pooling.
What's Missing?
- PropType Validation: Not everyone uses PropTypes, so they aren't part of Preact's core.
- PropTypes are fully supported in preact-compat, or you can use them manually.
- Children: Not necessary in Preact, because
props.children
is always an Array.React.Children
is fully supported in preact-compat.
- Synthetic Events: Preact's browser support target does not require this extra overhead.
- Preact uses the browser's native
addEventListener
for event handling. See GlobalEventHandlers for a full list of DOM event handlers. - A full events implementation would mean more maintenance and performance concerns, and a larger API.
- Preact uses the browser's native
What's Different?
Preact and React have some more subtle differences:
render()
accepts a third argument, which is the root node to replace, otherwise it appends. This may change slightly in a future version, perhaps auto-detecting that a replacement render is appropriate by inspecting the root node.- Components do not implement
contextTypes
orchildContextTypes
. Children receive allcontext
entries drawn fromgetChildContext()
.