svelte-kit preview throws "Cannot destructure property 'cancelable' of 'undefined' as it is undefined" during dispatch custom event call.

[bhvngt]

Describe the bug

while dispatching a custom event, following error gets thrown.

index-e29e855b.js:304 Uncaught TypeError: Cannot destructure property 'cancelable' of 'undefined' as it is undefined.
    at index-e29e855b.js:304:27
    at HTMLButtonElement.decrease (index.svelte-50532f6b.js:84:5)

This happens only when I run svelte-kit build && svelte-kit preview. Its little baffling because svelte source code correctly defines default parameter to the third parameter. However, on build, the default value gets stripped out. I tried with non-minified build also and see the same result.

Workaround: Currently a simple workaround is to pass an empty third parameter to dispatch method.

Reproduction

https://stackblitz.com/edit/sveltejs-kit-template-default-9twecw?file=src/lib/Counter.svelte

On the console, cancel the svelte-kit dev process and then start npm run build && npm run preview command.

When - or + button is clicked, a custom dispatch event is called. ideally it should print the show the current count in the parent component. However, on my browser, above error is thrown.

Logs

index-e29e855b.js:304 Uncaught TypeError: Cannot destructure property 'cancelable' of 'undefined' as it is undefined.
    at index-e29e855b.js:304:27
    at HTMLButtonElement.decrease (index.svelte-50532f6b.js:84:5)

System Info

System:
    OS: macOS 12.3.1
    CPU: (10) arm64 Apple M1 Pro
    Memory: 75.91 MB / 32.00 GB
    Shell: 3.4.1 - /opt/homebrew/bin/fish
  Binaries:
    Node: 18.1.0 - ~/Library/Caches/fnm_multishells/69089_1652879820227/bin/node
    Yarn: 1.22.15 - ~/Library/Caches/fnm_multishells/69089_1652879820227/bin/yarn
    npm: 8.8.0 - ~/Library/Caches/fnm_multishells/69089_1652879820227/bin/npm
  Browsers:
    Chrome: 101.0.4951.64
    Chrome Canary: 104.0.5069.0
    Firefox: 99.0
    Firefox Developer Edition: 101.0
    Safari: 15.4
  npmPackages:
    @sveltejs/adapter-auto: next => 1.0.0-next.43
    @sveltejs/kit: next => 1.0.0-next.335
    svelte: ^3.48.0 => 3.48.0

Severity

annoyance

Additional Information

I thought of raising it in this repo, since the issue is happening during the svelte-kit build.

[lemmon]

Thank you! I've just spent several hours debugging my code.

I fould that the issue starts with SVELTE version 3.48.0. Everything works just fine with version up to 3.47.0.

I have my suspicion that it might have something to do with this feature:

Allow creating cancelable custom events with createEventDispatcher (sveltejs/svelte#4623)

[Conduitry]

Weird. I wonder whether we're running into a Rollup/Terser/esbuild optimization bug? The unoptimized code in createEventDispatcher does look like it would avoid this, as you noted.

[bluwy]

It looks like a regression in Rollup 2.74.0, specifically rollup/rollup#4498. I've created an issue there to track it: rollup/rollup#4507

[bluwy]

Update: Rollup 2.74.1 is released with a revert for the feature, until it's ironed out.

[yekta]

Having the same problem. Spent a couple of hours trying to understand what's going on but couldn't until I saw this issue. It's actually making some libraries not work in my case.

Edit: Tried with SvelteKit version 1.0.0-next.338 and error is gone.