@lit-labs/react

A React component wrapper for web components.

Usage no npm install needed!

<script type="module">
  import litLabsReact from 'https://cdn.skypack.dev/@lit-labs/react';
</script>

README

@lit-labs/react

React integration for Web Components and Reactive Controllers.

Overview

createComponent

While React can render Web Components, it cannot easily pass React props to custom element properties or event listeners.

This package provides a utility wrapper createComponent which makes a React component wrapper for a custom element class. The wrapper correctly passes React props to properties accepted by the custom element and listens for events dispatched by the custom element.

How it works

For properties, the wrapper interrogates the web component class to discover its available properties. Then any React props passed with property names are set on the custom element as properties and not attributes.

For events, createComponent accepts a mapping of React event prop names to events fired by the custom element. For example passing {onfoo: 'foo'} means a function passed via a prop named onfoo will be called when the custom element fires the foo event with the event as an argument.

Usage

Import React, a custom element class, and createComponent.

import * as React from 'react';
import {createComponent} from '@lit-labs/react';
import {MyElement} from './my-element.js';

export const MyElementComponent = createComponent(
  React,
  'my-element',
  MyElement,
  {
    onactivate: 'activate',
    onchange: 'change',
  }
);

After defining the React component, you can use it just as you would any other React component.

<MyElementComponent
  active={isActive}
  onactivate={(e) => (isActive = e.active)}
/>

useController

Reactive Controllers allow developers to hook a component's lifecycle to bundle together state and behavior related to a feature. They are similar to React hooks in the user cases and capabilities, but are plain JavaScript objects instead of functions with hidden state.

useController is a React hook that create and stores a Reactive Controller and drives its lifecycle using React hooks like useState and useLayoutEffect.

How it works

useController uses useState to create and store an instance of a controller and a ReactControllerHost. It then calls the controller's lifecycle from the hook body and useLayoutEffect callbacks, emulating the ReactiveElement lifecycle as closely as possible. ReactControllerHost implements addController so that controller composition works and nested controller lifecycles are called correctly. ReactControllerHost also implements requestUpdate by calling a useState setter, so that a controller with new renderable state can cause its host component to re-render.

Controller timings are implemented as follows:

Controller API React hook equivalent
constructor useState initial value
hostConnected useState initial value
hostDisconnected useLayoutEffect cleanup, empty deps
hostUpdate hook body
hostUpdated useLayoutEffect
requestUpdate useState setter
updateComplete useLayoutEffect

Usage

import * as React from 'react';
import {useController} from '@lit-labs/react/use-controller.js';
import {MouseController} from '@example/mouse-controller';

// Write a React hook function:
const useMouse = () => {
  // Use useController to create and store a controller instance:
  const controller = useController(React, (host) => new MouseController(host));
  // return the controller: return controller;
  // or return a custom object for a more React-idiomatic API:
  return controller.position;
};

// Now use the new hook in a React component:
const Component = (props) => {
  const mousePosition = useMouse();
  return (
    <pre>
      x: {mousePosition.x}
      y: {mousePosition.y}
    </pre>
  );
};

Installation

From inside your project folder, run:

$ npm install @lit-labs/react

Contributing

Please see CONTRIBUTING.md.