---
title: Event modifiers
---

DOM event handlers can have *modifiers* that alter their behaviour. For example, a handler with a `once` modifier will only run a single time:

```html
<script>
	function handleClick() {
		alert('no more alerts')
	}
</script>

<button on:click|once={handleClick}>
	Click me
</button>
```

The full list of modifiers:

* `preventDefault` — calls `event.preventDefault()` before running the handler. Useful for client-side form handling, for example.
* `stopPropagation` — calls `event.stopPropagation()`, preventing the event reaching the next element
* `passive` — improves scrolling performance on touch/wheel events (Svelte will add it automatically where it's safe to do so)
* `capture` — fires the handler during the *capture* phase instead of the *bubbling* phase ([MDN docs](https://developer.mozilla.org/en-US/docs/Learn/JavaScript/Building_blocks/Events#Event_bubbling_and_capture))
* `once` — remove the handler after the first time it runs
* `self` — only trigger handler if event.target is the element itself

You can chain modifiers together, e.g. `on:click|once|capture={...}`.
