mirror of https://github.com/sveltejs/svelte
feat: provide `MediaQuery` / `prefersReducedMotion` (#14422)
* feat: provide `MediaQuery` / `prefersReducedMotion` closes #5346 * matches -> current, server fallback * createStartStopNotifier * test polyfill * more tests fixes * feedback * rename * tweak, types * hnnnggh * mark as pure * fix type check * notify -> subscribe * add links to inline docs * better API, more docs * add example to prefersReducedMotion * add example for MediaQuery * typo * fix example * tweak docs * changesets * note when APIs were added * add note * regenerate --------- Co-authored-by: Rich Harris <rich.harris@vercel.com>pull/14570/head
Simon H
10 months ago
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GitHub
parent
73b3cf72d0
commit
0a9890bb1e
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---
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'svelte': minor
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---
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feat: add `createSubscriber` function for creating reactive values that depend on subscriptions
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---
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'svelte': minor
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---
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feat: add reactive `MediaQuery` class, and a `prefersReducedMotion` class instance
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@ -1,2 +1,32 @@
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import { MediaQuery } from 'svelte/reactivity';
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export * from './spring.js';
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export * from './tweened.js';
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/**
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* A [media query](https://svelte.dev/docs/svelte/svelte-reactivity#MediaQuery) that matches if the user [prefers reduced motion](https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-reduced-motion).
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*
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* ```svelte
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* <script>
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* import { prefersReducedMotion } from 'svelte/motion';
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* import { fly } from 'svelte/transition';
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*
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* let visible = $state(false);
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* </script>
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*
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* <button onclick={() => visible = !visible}>
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* toggle
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* </button>
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*
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* {#if visible}
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* <p transition:fly={{ y: prefersReducedMotion.current ? 0 : 200 }}>
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* flies in, unless the user prefers reduced motion
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* </p>
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* {/if}
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* ```
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* @type {MediaQuery}
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* @since 5.7.0
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*/
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export const prefersReducedMotion = /*@__PURE__*/ new MediaQuery(
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'(prefers-reduced-motion: reduce)'
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);
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import { get, tick, untrack } from '../internal/client/runtime.js';
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import { effect_tracking, render_effect } from '../internal/client/reactivity/effects.js';
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import { source } from '../internal/client/reactivity/sources.js';
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import { increment } from './utils.js';
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/**
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* Returns a `subscribe` function that, if called in an effect (including expressions in the template),
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* calls its `start` callback with an `update` function. Whenever `update` is called, the effect re-runs.
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*
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* If `start` returns a function, it will be called when the effect is destroyed.
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*
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* If `subscribe` is called in multiple effects, `start` will only be called once as long as the effects
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* are active, and the returned teardown function will only be called when all effects are destroyed.
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*
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* It's best understood with an example. Here's an implementation of [`MediaQuery`](https://svelte.dev/docs/svelte/svelte-reactivity#MediaQuery):
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*
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* ```js
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* import { createSubscriber } from 'svelte/reactivity';
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* import { on } from 'svelte/events';
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*
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* export class MediaQuery {
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* #query;
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* #subscribe;
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*
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* constructor(query) {
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* this.#query = window.matchMedia(`(${query})`);
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*
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* this.#subscribe = createSubscriber((update) => {
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* // when the `change` event occurs, re-run any effects that read `this.current`
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* const off = on(this.#query, 'change', update);
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*
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* // stop listening when all the effects are destroyed
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* return () => off();
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* });
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* }
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*
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* get current() {
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* this.#subscribe();
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*
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* // Return the current state of the query, whether or not we're in an effect
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* return this.#query.matches;
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* }
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* }
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* ```
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* @param {(update: () => void) => (() => void) | void} start
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* @since 5.7.0
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*/
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export function createSubscriber(start) {
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let subscribers = 0;
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let version = source(0);
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/** @type {(() => void) | void} */
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let stop;
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return () => {
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if (effect_tracking()) {
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get(version);
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render_effect(() => {
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if (subscribers === 0) {
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stop = untrack(() => start(() => increment(version)));
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}
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subscribers += 1;
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return () => {
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tick().then(() => {
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// Only count down after timeout, else we would reach 0 before our own render effect reruns,
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// but reach 1 again when the tick callback of the prior teardown runs. That would mean we
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// re-subcribe unnecessarily and create a memory leak because the old subscription is never cleaned up.
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subscribers -= 1;
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if (subscribers === 0) {
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stop?.();
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stop = undefined;
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}
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});
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};
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});
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}
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};
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}
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import { createSubscriber } from './create-subscriber.js';
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import { on } from '../events/index.js';
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/**
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* Creates a media query and provides a `current` property that reflects whether or not it matches.
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*
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* Use it carefully — during server-side rendering, there is no way to know what the correct value should be, potentially causing content to change upon hydration.
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* If you can use the media query in CSS to achieve the same effect, do that.
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*
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* ```svelte
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* <script>
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* import { MediaQuery } from 'svelte/reactivity';
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*
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* const large = new MediaQuery('min-width: 800px');
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* </script>
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*
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* <h1>{large.current ? 'large screen' : 'small screen'}</h1>
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* ```
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* @since 5.7.0
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*/
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export class MediaQuery {
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#query;
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#subscribe = createSubscriber((update) => {
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return on(this.#query, 'change', update);
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});
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get current() {
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this.#subscribe();
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return this.#query.matches;
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}
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/**
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* @param {string} query A media query string
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* @param {boolean} [matches] Fallback value for the server
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*/
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constructor(query, matches) {
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// For convenience (and because people likely forget them) we add the parentheses; double parentheses are not a problem
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this.#query = window.matchMedia(`(${query})`);
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}
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}
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