Svelte模板语法

use:

操作是在安装元素时调用的函数。它们是使用 use: 指令添加的，并且通常使用 $effect，以便它们可以在卸载元素时重置任何状态：

¥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:

App

<script>
	/** @type {import('svelte/action').Action} */
	function myaction(node) {
		// the node has been mounted in the DOM

		$effect(() => {
			// setup goes here

			return () => {
				// teardown goes here
			};
		});
	}
</script>

<div use:myaction>...</div>

<script lang="ts">
	import type { Action } from 'svelte/action';

	const myaction: Action = (node) => {
		// the node has been mounted in the DOM

		$effect(() => {
			// setup goes here

			return () => {
				// teardown goes here
			};
		});
	};
</script>

<div use:myaction>...</div>

可以使用参数调用操作：

¥An action can be called with an argument:

App

<script>
	/** @type {import('svelte/action').Action} */
	function myaction(node, data) {
		// ...
	}
</script>

<div use:myaction={data}>...</div>

<script lang="ts">
	import type { Action } from 'svelte/action';

	const myaction: Action = (node, data) => {
		// ...
	};
</script>

<div use:myaction={data}>...</div>

该操作仅调用一次（但不是在服务器端渲染期间） - 如果参数发生变化，它将不会再次运行。

¥The action is only called once (but not during server-side rendering) — it will not run again if the argument changes.

Legacy mode
在 $effect 符文之前，操作可以返回具有 update 和 destroy 方法的对象，其中如果参数发生变化，将使用参数的最新值调用 update。最好使用效果。

¥[!LEGACY] 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.

类型(Typing)

¥Typing

Action 接口接收三个可选类型参数 — 节点类型（如果操作适用于所有内容，则可以是 Element）、参数以及由操作创建的任何自定义事件处理程序：

¥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:

App

<script>
	/**

	 * @type {import('svelte/action').Action<

	 * 	HTMLDivElement,

	 * 	undefined,

	 * 	{

	 * 		onswiperight: (e: CustomEvent) => void;

	 * 		onswipeleft: (e: CustomEvent) => void;

	 * 		// ...

	 * 	}

	 * >}
	 */
	function gestures(node) {
		$effect(() => {
			// ...
			node.dispatchEvent(new CustomEvent('swipeleft'));

			// ...
			node.dispatchEvent(new CustomEvent('swiperight'));
		});
	}
</script>

<div
	use:gestures
	onswipeleft={next}
	onswiperight={prev}
>...</div>

<script lang="ts">
	import type { Action } from 'svelte/action';

	const gestures: Action<

		HTMLDivElement,

		undefined,

		{

			onswiperight: (e: CustomEvent) => void;

			onswipeleft: (e: CustomEvent) => void;

			// ...

		}

	> = (node) => {
		$effect(() => {
			// ...
			node.dispatchEvent(new CustomEvent('swipeleft'));

			// ...
			node.dispatchEvent(new CustomEvent('swiperight'));
		});
	};
</script>

<div
	use:gestures
	onswipeleft={next}
	onswiperight={prev}
>...</div>

bind: transition: