fix(svelte): prevent empty class attribute with null defaults#15604
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ematipico merged 9 commits intoMar 26, 2026
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ematipico
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| // Remove empty class="" attributes from SSR output to match native Svelte behavior. | ||
| // This happens when components extract class with null defaults: let { class: className = null } | ||
| // Svelte 5 SSR renders null class values as class="", but standalone Svelte omits them. |
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This is a svelte bug, which is worth tracking. You might want rewording you comment and add the issue #15576
ematipico
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Feb 23, 2026
| "@astrojs/svelte": patch | ||
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| fix(svelte): prevent empty class attribute with null defaults |
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Suggested change
| fix(svelte): prevent empty class attribute with null defaults | |
| Adds a temporary workaround caused by empty class attributes. |
Fixes withastro#15576 When Svelte components extract the class property with a null default (e.g., `let { class: className = null } = $props();`), Svelte 5's SSR render function outputs `class=""` instead of omitting the attribute entirely. This fix post-processes the SSR HTML output to remove empty class attributes, matching native Svelte behavior where null/undefined class values don't render the attribute. The fix uses a simple regex to strip ` class=""` from the rendered HTML. This approach is safe because: - It only matches the exact pattern of a space followed by class="" - It doesn't affect non-empty class attributes - It runs after Svelte's render function completes Added comprehensive tests covering both build and dev modes.
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Fixes #15576
This adds a temporary workaround for a Svelte bug where components extract the class property with a null default (like
let { class: className = null } = $props();). The SSR output incorrectly rendersclass=""instead of omitting the attribute entirely.The fix post-processes the SSR HTML output to remove empty class attributes, matching native Svelte behavior until the upstream issue is resolved.
Tests verify the fix works correctly in both build and dev modes.