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:

  1. <script>
  2.     function handleClick() {
  3.         alert('no more alerts')
  4.     }
  5. </script>
  7. <button on:click|once={handleClick}>
  8.     Click me
  9. </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)
  • once — remove the handler after the first time it runs

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