[LiveComponent] Return empty string for data-value="" instead of falling back to null

[mercuryseries]

Q	A
Bug fix?	yes
New feature?	no
Docs?	no
Issues	#
License	MIT

Problem

Demo video

before.mov

<input type="text" data-model="post.title">
<button
    type="button"
    data-model="post.title"
    data-value="" <!-- HERE -->
    data-action="live#update"
>
    Clear Title
</button>

When using data-value="" on an element, the current implementation incorrectly returns null instead of the intended empty string value. This happens because the condition if (element.dataset.value) evaluates to false for empty strings (since empty strings are falsy in JavaScript), causing the function to fall through to the final return null; statement.

Impact

This behavior prevents developers from explicitly setting empty string values via the data-value attribute, which is a common use case for clearing form fields or resetting values to empty states rather than null.

Current behavior:

<button data-model="title" data-value="" data-action="live#update">Clear</button>
<!-- Results in: null -->

Expected behavior:

<button data-model="title" data-value="" data-action="live#update">Clear</button>  
<!-- Should result in: "" -->

After (demo video)

after.mov

Changes

Replace the truthiness check if (element.dataset.value) with an explicit attribute existence check if (element.hasAttribute("data-value")). This ensures that any data-value attribute, including those with empty string values, are properly processed and returned.

Manual testing done

• ✅ data-value="" now returns ""
• ✅ data-value="test" still returns "test"
• ✅ Missing data-value attribute still falls back to other value sources
• ✅ All existing functionality remains intact

[github-actions]

📊 Packages dist files size difference

ℹ️ No difference in dist packagesFiles.

[smnandre]

👍

It would indeed be consistent with Stimulus values https://stimulus.hotwired.dev/reference/values#getters

Could you add some tests to prevent any future regression ?

[mercuryseries]

@smnandre I added some tests. I see that some tests failed, but seems not related with the changes. Can you confirm please?

[smnandre]

It does not feel related to me.. @Kocal wdyt ?

[Kocal]

No that's not related, it should be green after a rebase

[Kocal]

Thank you @mercuryseries.