Svelte 5: Index is undefined within a #each loop on a element with a transition

[chainlist]

Describe the bug

Hello everyone,

I found a bug when using an #each...as... block with an animation on the element.

When looping through a collection and getting the index of the items while having a transition on the element returns an undefined index after the animation got triggered. But not always.

Reproduction

You can reproduce the issue on this REPL. The bug is not visible right away you have to trigger the animation by clicking on the buttons.

https://svelte-5-preview.vercel.app/#H4sIAAAAAAAACn1T0W7bMAz8FU4bahvwkrXF9uA6AfaYb4jzoFnyRkyRDIkOGgj-94lWgqZBMfjBIH28O53oKAY0OohmH4WVRy0a8XMcRS3oPHIRTtqQTnVwk--504be40jbznaEx9F5gghBG92T8zDD4N0RijxXvLxDDVLpO8SavLQBCZ0tGGs0AZI-BtjAl0CSdLnnfkcRUDXwWAPbbKATuwSDx07UoJxNnUGakOjrW_jTHfzpDU5-ukc_36GfPyY_VHysi1nOic3uCwYWNRTklOO3NKY4LAH0zoaMTMBrVGUG3nKlqyDttdpdA1Da40mrcklklT-XCJstxOwbByiZd4WhzAYqeHiAT7jiogKvafI2u3_5YCRb4JH_TFxaHNjSmSs23a7fFsG2Ck_QGxnCpltWJ3Ri2ZD4Wcv-zyUlGYDmzNn-moicBWd7g_3fTSwrPtZiLGgqqZq3keZ2nXGZa81cM0snuaw7mVuZ9wEmOQ6uBoQlweqqbRDcRA2v4yZGUJOXvIBpu75_gzkJM3rFqzDDV9hZpV8biJjcGLx3kg3cPG2gs9ELbJWPfbkrhWE08px2yejXS7S_5ZhUf4y5XgjzePrjjk7hgFqJhpOfD_M_s5STGKwDAAA=

Logs

No log in the console

System Info

System:
    OS: Windows 11 10.0.22621
    CPU: (20) x64 12th Gen Intel(R) Core(TM) i7-12700H
    Memory: 16.27 GB / 31.68 GB
  Binaries:
    Node: 18.13.0 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.22.19 - C:\Program Files (x86)\Yarn\bin\yarn.CMD
    npm: 8.19.3 - C:\Program Files\nodejs\npm.CMD
    pnpm: 8.3.1 - ~\AppData\Roaming\npm\pnpm.CMD
  Browsers:
    Edge: Chromium (119.0.2151.58)
    Internet Explorer: 11.0.22621.1

Severity

annoyance

[eddiemcconkie]

Looks like the selector API got removed recently - #9426

Not sure how that affects your issue

[chainlist]

Indeed, the issue was caused by the used of the selector api.

I updated my REPL with own custom Selector and it seems to work fine with it.
Guess it's an issue closed.

Said REPL:
https://svelte-5-preview.vercel.app/#H4sIAAAAAAAACo1Uy27bMBD8la1aRBKgyk2C9iA_gB5z7tHygRGphC1NCuQqtSHo38slLct2g6LwQSA5OzscznpIWqmES6rtkGi2F0mVfO-6pEjw2NHCvQmFwq-d6W1DOyvXWNnhptY1yn1nLMIATijRoLEwQmvNHtJyMW2VkSJdXhW0jIszOCIWaJl2EqXRKWGVQJAo9g7W8MkhQ5Ftab_GASSv4L4AUlxBnTx5GNzXSQHcaL_TMuU8fXEJf7iBP8xwtP0t-vEG_fg--S6na53EkmUkdpsSMC0gRcMNfZlS6S4Y0BjtItIDJ4uyCLzk8q-Cwgr-NBnAhZVvgmfBkTIeZxLWGxiibtlCRryldFkUkMPdHXyQJS1ysAJ7q6P65TslUQKV_KPitEWGhZ0xJ9GrxZwJveLyDRrFnFvXIUWuTkJYho-CNa8nl5gDHCPn6rlHNBqMbpRsfq2HLKdrBWFOYIb5uBlwXC0iLnItiGuk1r5d7NuryzbXBvp2ZFwBEoKD-dRbSTA9VhTH9TAA7y2jAPp0ff0Co29M6JKiMMJneNJcHCoYpFej5K2SKODit3J4VCLAynjt01tx6TrFjj5LShxO1r6wznf91sV1IIzlfvj2hstWCp5U5PxYnGf1Zsjmuf3pLmc2PAf8mIY0qGh6a4XGebim-IWI2j4Ek9mXfBKNr9KVc5U_mpTSh17q_9E-cJfgKVZXNVdFoU4cwr9H2-uGHmmen5nrxKTF7_N1w-kyUPxt5W78A7XIBLACBQAA

[chainlist]

Said MR #9426 "fixed" the issue.

In fact, the issue was caused by the selector API and not the loop block + transition.