Reactive Statement

<script>
  $: if (count >= 10) {
    alert('count is dangerously high!')
    count = 9
  }

  let foo, bar, baz

  $: quux = foo + bar
  $: console.log(quux)

  $: {
    // block expression
  }

  $: if (quux > 10) {
    // actually any ->
  } else {
    // js expression
  }

  $: for (let i = 0; i < baz; i++) {
    // any js expression
  }

  // function declaration too
  $: grunt = arg => quux / arg * baz

  $: { // this would also work
    if (quux < 10) break $
    baz++
  }

  $: (async () => { // and even this
    bar = await Promise.resolve(foo%2)
  })()
</script>