once not working

[thisispete]

when I use once and on:intersect the function seems to be getting called every frame instead of just one time.

  const doOnce = () => {
    console.log('once?');
    //this is firing every frame
  };
  
  ...
  
  <IntersectionObserver once {element} on:intersect={doOnce}>
  <div bind:this={element}>
  
  ...

[thisispete]

oh.. ok something just noticed: it fires every time the contents changes - so I have a tweened element inside, it fires every frame until the animation ends, and then it stops firing.

ie:

  const number = tweened(0, {
    duration: 5000
  });
  
  const doOnce = () => {
    console.log('once?');
    $number = 15000
  }

<IntersectionObserver once {element} on:intersect={doOnce}>
<div bind:this={element}>
  {$number}

this also messes with the duration of the tween - as a side effect, it's resetting every frame, so it takes much longer the bigger the number or the more decimal places.

[metonym]

Could you provide a minimal repro? https://svelte.dev/playground/hello-world?version=5.2.0

Is this using Svelte 5? Happy to help debug.