let visible = true
  let prevScrollPos = window.pageYOffset
  const handleScroll = event => {
    let thisScrollPos = window.pageYOffset
    visible = thisScrollPos < prevScrollPos
    prevScrollPos = thisScrollPos
  }
  onMount(() => window.addEventListener('scroll', handleScroll))
  onDestroy(() => window.removeEventListener('scroll', handleScroll))

<script>
  let visible = true;
</script>
{#if visible}
    <p>Some text</p>
{/if}