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

	function handleClick() {
		alert('no more alerts');

<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)
  • nonpassive — explicitly set passive: false
  • capture — fires the handler during the capture phase instead of the bubbling phase (MDN docs)
  • once — remove the handler after the first time it runs
  • self — only trigger handler if is the element itself
  • trusted — only trigger handler if event.isTrusted is true. I.e. if the event is triggered by a user action.

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