set_custom_element_data: Cannot use 'in' operator to search for 'item' in undefined

[TommasoAmici]

Describe the bug

After upgrading from 3.44.2 to 3.44.3 one of the components I work on has broken with this error.

We use svelte to output custom elements.

Reproduction

https://github.com/TommasoAmici/svelte-error

Logs

Uncaught TypeError: Cannot use 'in' operator to search for 'item' in undefined

function set_custom_element_data(node, prop, value) {
    if (prop in node) {
        node[prop] = typeof node[prop] === 'boolean' && value === '' ? true : value;
    }
    else {
        attr(node, prop, value);
    }
}

System Info

System:
    OS: macOS 11.6
    CPU: (16) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 706.83 MB / 32.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 16.13.1 - /usr/local/Cellar/node@16/16.13.1/bin/node
    Yarn: 1.22.17 - /usr/local/bin/yarn
    npm: 8.1.2 - /usr/local/Cellar/node@16/16.13.1/bin/npm
    Watchman: 2021.12.20.00 - /usr/local/bin/watchman
  Browsers:
    Chrome: 96.0.4664.110
    Edge: 96.0.1054.62
    Firefox Developer Edition: 96.0
    Safari: 15.2
    Safari Technology Preview: 15.4
  npmPackages:
    rollup: ^2.61.1 => 2.61.1 
    svelte: ^3.44.3 => 3.44.3

Severity

blocking an upgrade

[ssuess]

This is also blocking for me. Is there any response or update? Thanks!

[TommasoAmici]

This is still happening as of 3.46.6

[abdullahkamran]

We maintain a library of web components made in Svelte, and this issue is blocking an upgrade for us.

This issue seems to have been introduced with this PR:
https://github.com/sveltejs/svelte/pull/6073

[ssuess]

Is there no fix for this yet?

[geoffrich]

Is someone able to provide a smaller reproduction for this? The linked repo contains 400+ lines of component code and Storybook, which will make it difficult to pinpoint the issue.

I doubt it was introduced by #6073, since a) the error is thrown before the line that PR changed and b) that change was released in 3.38.0, where this issue was introduced with 3.44.3.

[imperator-maximus]

Any progress on this issue? As a workaround I am doing for every array refresh instead of list=list

    setTimeout(function() {           
        list=list
        },200)  

in my project. I have this now on many places in my application - makes current Svelte version not very usable to be honest.

[ssuess]

In case this helps anyone we are testing a fix (that has its own issues still) where we replace our repeating component with <svelte:self > and it seems promising

[geoffrich]

@imperator-maximus @ssuess please see my comment above - we need a smaller reproduction to properly investigate this issue.

[imperator-maximus]

I cannot provide one: it seems that this only occurs in very large projects. If projects are smaller I never had such an issue.