React's Hooks API but for standard web components and lit-html.
<!doctype html>
<html lang="en">
<my-counter></my-counter>
<script type="module">
import { html } from 'https://unpkg.com/lit-html/lit-html.js';
import { component, useState } from 'https://unpkg.com/@matthewp/haunted/haunted.js';
function Counter() {
const [count, setCount] = useState(0);
return html`
<div id="count">${count}</div>
<button type="button" @click=${() => setCount(count + 1)}>Increment</button>
`;
}
customElements.define('my-counter', component(Counter));
</script>A starter app is available on codesandbox and also can be cloned from this repo. This app gives you the basics of how to use Haunted and build components.
Currently Haunted is available as the @matthewp/haunted package. In the future I hope to get the non-scoped name.
npm install @matthewp/hauntedHaunted comes in a few builds. Pick one based on your chosen environment:
- index.js is available for bundlers such as Webpack and Rollup. Use with:
import { useState } from '@matthewp/haunted';; - web.js is avaible for use with the web's native module support. Use with:
import { useState } from '../node_modules/@matthewp/haunted/web.js';. - haunted.js is available via the CDN unpkg. This is great for small apps or for local development without having to install anything. Use with
import { useState } from 'https://unpkg.com/@matthewp/haunted/haunted.js';
Haunted supports the same API as React Hooks. My hope is that by doing so you can reuse hooks available on npm simply by aliasing package names in your bundler's config.
Currently Haunted supports the following hooks:
Create a tuple of state and a function to change that state.
const [count, setCount] = useState(0);Useful for side-effects that run after the render has been commited.
<!doctype html>
<my-counter></my-counter>
<script type="module">
import { html } from 'https://unpkg.com/lit-html/lit-html.js';
import { component, useState, useEffect } from 'https://unpkg.com/@matthewp/haunted/haunted.js';
function Counter() {
const [count, setCount] = useState(0);
useEffect(() => {
document.title = `Clicked ${count} times`;
});
return html`
<div id="count">${count}</div>
<button type="button" @click=${() => setCount(count + 1)}>Increment</button>
`;
}
customElements.define('my-counter', component(Counter));
</script>Like useMemo, useEffect can take a second argument that are values that are memoized. The effect will only run when these values change.
function App() {
let [name, setName] = useState('Dracula');
useEffect(() => {
// This only occurs when name changes.
document.title = `Hello ${name}`;
}, [name]);
return html`...`;
}Since effects are used for side-effectual things and might run many times in the lifecycle of a component, useEffect supports returning a teardown function.
An example of when you might use this is if you are setting up an event listener.
function App() {
let [name, setName] = useState('Wolf Man');
useEffect(() => {
function updateNameFromWorker(ev) {
setName(ev.data);
}
worker.addEventListener('message', updateNameFromWorker);
return () => {
worker.removeEventListener('message', updateNameFromWorker);
}
});
return html`...`;
}Create state that updates after being ran through a reducer function.
<!doctype html>
<my-counter></my-counter>
<script type="module">
import { html } from 'https://unpkg.com/lit-html/lit-html.js';
import { component, useReducer } from 'https://unpkg.com/@matthewp/haunted/haunted.js';
const initialState = {count: 0};
function reducer(state, action) {
switch (action.type) {
case 'reset': return initialState;
case 'increment': return {count: state.count + 1};
case 'decrement': return {count: state.count - 1};
}
}
function Counter() {
const [state, dispatch] = useReducer(reducer, initialState);
return html`
Count: ${state.count}
<button @click=${() => dispatch({type: 'reset'})}>
Reset
</button>
<button @click=${() => dispatch({type: 'increment'})}>+</button>
<button @click=${() => dispatch({type: 'decrement'})}>-</button>
`;
}
customElements.define('my-counter', component(Counter));
</script>Create a memoized state value. Only reruns the function when dependent values have changed.
<!doctype html>
<my-app></my-app>
<script type="module">
import { html } from 'https://unpkg.com/lit-html/lit-html.js';
import { component, useMemo, useState } from 'https://unpkg.com/@matthewp/haunted/haunted.js';
function fibonacci(num) {
if (num <= 1) return 1;
return fibonacci(num - 1) + fibonacci(num - 2);
}
function App() {
const [value, setVal] = useState(12);
const fib = useMemo(() => fibonacci(value), [value]);
return html`
<h1>Fibonacci</h1>
<input type="text" @change=${ev => setVal(Number(ev.target.value))} value="${value}">
<div>Fibonacci <strong>${fib}</strong></div>
`;
}
customElements.define('my-app', component(App));
</script>BSD-2-Clause
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