Linked State

Jason Miller edited this page Jan 26, 2016 · 1 revision

One area Preact takes a little further than React is in optimizing state changes. A common pattern in ES2015 React code is to use Arrow functions within a render() method in order to update state in response to events. Creating functions enclosed in a scope on every render is inefficient and forces the garbage collector to do more work than is necessary.

The Nicer Manual Way

One solution to this is to bind component methods declaratively, using ES7 decorators. Here is an example using decko:

class Foo extends Component {
	@bind
	updateText(e) {
		this.setState({ text: e.target.value });
	}
	render({ }, { text }) {
		return <input value={text} onInput={this.updateText} />;
	}
}

While this achieves much better runtime performance, it's still a lot of unnecessary code to wire up state to UI.

Linked State to the Rescue

Fortunately, there is a solution in the form of preact's linkState(), available as a method on the Component class.

Calling .linkState('text') returns a handler function that, when passed an Event, uses its associated value to update the named property in your component's state. Multiple calls to linkState(name) with the same name are cached, so there is essentially no performance penalty.

Here is the previous example rewritten using Linked State:

class Foo extends Component {
	render({ }, { text }) {
		return <input value={text} onInput={this.linkState('text')} />;
	}
}

This is concise, easy to comprehend, and effective. It handles linking state from any input type. An optional second argument 'path' can be used to explicitly provide a dot-notated keypath to the new state value for more custom bindings (such as binding to a third party component's value).

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