Build finish successfully but get stuck and not exit

Describe the bug When running yarn build the build finishes successfully but does not exit. This cause an issue with automating builds.

To Reproduce I have boiled down the issue to having setInterval in a script.

<script>
  let time = 1;
  setInterval(() => {
    time += 1;
  }, 1000);
</script>

{time}

A solution to this is of course to use onMount

<script>
  import { onMount } from "svelte";

  let time = 1;
  onMount(() => {
    setInterval(() => {
      time += 1;
    }, 1000);
  })
</script>

{time}

Expected behavior I’m not sure if this is expected behavior or not but, In Sapper this did not happen, the first snippet of code run just fine.

Severity Not severe since there is a workaround but I think it maybe need to be documented.

[mattpilott]

this works with the new structure:

adapter: {
   adapt: static
},

[Conduitry]

Interesting. I’m not entirely sure why it’s causing a hang in SvelteKit but not in Sapper. But, regardless, having a setInterval without a clearInterval is a bad idea, because of memory leaks. And that’s especially a problem on the server, where every single time someone loads a page that contains that component, it creates another setInterval, which then hangs around forever.

I think the path forward here is not to make it not hang, but to do something to warn people that this is a bad thing to be doing. In SSR, there’s not really a reason to be creating an interval (or a timeout) at all, because it’s not going to fire until after the SSR’d HTML is rendered. I don’t know what’s an effective way to warn about this. Static analysis won’t really help. Do we override these globals with our own versions, and display a warning if we detect that one is being run during the synchronous period that the server-side rendering is happening? I’m not sure.