svelte-template-directives

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Svelte Template Directives

@attach (Svelte 5.29+)

The reactive alternative to `use:` actions. Re-runs when dependencies change, passes through components via spread, supports cleanup functions.

svelte

<script>
	import ImageZoom from 'js-image-zoom';

	function useZoom(options) {
		return (element) => {
			new ImageZoom(element, options);
			return () => console.log('cleanup');
		};
	}
</script>

<!-- Re-runs if options changes (use: wouldn't!) -->
<figure {@attach useZoom({ width: 400 })}>
	<img src="photo.jpg" alt="zoomable" />
</figure>

Quick Reference

Directive	Purpose	Reactive?
`{@attach}`	DOM manipulation, 3rd-party	Yes
`{@html}`	Render raw HTML strings	Yes
`{@render}`	Render snippets	Yes
`{@const}`	Local constants in blocks	N/A
`{@debug}`	Pause debugger on value change	N/A
`{#each (key)}`	Keyed iteration (always key!)	Yes
`<svelte:window>`	Window event listeners	N/A

@attach vs use: Actions

Feature	`use:`	`@attach`
Re-runs on arg change	No	Yes
Composable	Limited	Fully
Pass through props	Manual	Auto via spread
Convert legacy	N/A	`fromAction()`

Reference Files

attach-patterns.md - Real-world @attach

examples

other-directives.md - @html, @render,

@const, @debug

Notes

@attach requires Svelte 5.29+
Use fromAction from svelte/attachments to convert legacy actions
Attachments pass through wrapper components when you spread props
Always use keyed each blocks — never use index as key
Use <svelte:window>/<svelte:document> for global events, not $effect
Last verified: 2026-03-12

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