Memory leak on component unmount

[markpsiano]

Describe the bug

When a component is unmounted, event listeners which were attached to document on component mount are not removed. This leads to a memory leak as there are unused event listeners leftover after components unmount.

This can be verified by using chrome devtools, and taking heap snapshots at various points throughout page navigation/components mounting and unmounting, where the number of event listeners increases over time. It can also be verified in elements -> event listeners tab in devtools, where there are an increasing number of listeners upon mounting and unmounting components.

Fix is here: #12101

I'm not sure if this is the correct way of reporting an issue (making a fix as well as issue ticket), but just wanted more visibility here. If not, feel free to close this one.

Reproduction

Call unmount() on a component, observe how document event listeners are still retained, number of event listeners in memory using chrome memory devtools will show increasing amount as components are unmounted

Logs

No response

System Info

System:
    OS: macOS 12.2.1
    CPU: (10) arm64 Apple M1 Pro
    Memory: 75.61 MB / 32.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 20.13.1 - /usr/local/bin/node
    npm: 10.5.2 - /usr/local/bin/npm
  Browsers:
    Chrome: 126.0.6478.62
    Safari: 15.3
  npmPackages:
    rollup: ^4.18.0 => 4.18.0 
    svelte: 5.0.0-next.155 => 5.0.0-next.155

Severity

annoyance

[trueadm]

Closed with #12105. Thanks also for putting up a fix! Sorry I missed it originally – it's quite rare for someone to put up an issue and link to the fix at the same time :)

[mcullifer]

I am still experiencing this issue. Despite the element unmounting (navigating to a new page) it still seems to hold memory of an object used in an onclick function. In my case it's a very very large object so this is problematic. The onclick prop of my Button is from svelte/elements HTMLButtonAttributes rest props. The component has an optional prop for performing actions on close which is why this button does onClose?.(image). It also has the CSSTransition thing which mean it could be related to #15203 . Not sure what to do to get around this.

[trueadm]

It's almost impossible to fix this without some form of reproduction.