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82 lines
1.9 KiB
82 lines
1.9 KiB
4 weeks ago
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---
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title: use:
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---
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Actions are functions that are called when an element is mounted. They are added with the `use:` directive, and will typically use an `$effect` so that they can reset any state when the element is unmounted:
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```svelte
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<!--- file: App.svelte --->
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<script>
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/** @type {import('svelte/action').Action} */
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function myaction(node) {
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// the node has been mounted in the DOM
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$effect(() => {
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// setup goes here
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return () => {
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// teardown goes here
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};
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});
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}
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</script>
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<div use:myaction>...</div>
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```
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An action can be called with an argument:
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```svelte
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<!--- file: App.svelte --->
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<script>
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/** @type {import('svelte/action').Action} */
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function myaction(node, +++data+++) {
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// ...
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}
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</script>
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<div use:myaction={+++data+++}>...</div>
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```
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The action is only called once (but not during server-side rendering) — it will _not_ run again if the argument changes.
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> [!LEGACY]
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> Prior to the `$effect` rune, actions could return an object with `update` and `destroy` methods, where `update` would be called with the latest value of the argument if it changed. Using effects is preferred.
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## Typing
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The `Action` interface receives three optional type arguments — a node type (which can be `Element`, if the action applies to everything), a parameter, and any custom event handlers created by the action.:
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```svelte
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<!--- file: App.svelte --->
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<script>
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import { on } from 'svelte/events';
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/**
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* @type {import('svelte/action').Action<
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* HTMLDivElement,
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* null,
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* {
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* onswiperight: (e: CustomEvent) => void;
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* onswipeleft: (e: CustomEvent) => void;
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* // ...
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* }>}
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*/
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function gestures(node) {
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$effect(() => {
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// ...
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node.dispatchEvent(new CustomEvent('swipeleft'));
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// ...
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node.dispatchEvent(new CustomEvent('swiperight'));
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});
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}
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</script>
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<div
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use:gestures
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onswipeleft={next}
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onswiperight={prev}
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>...</div>
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```
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