fix(preact): stale prop updater keeps writing to the DOM after all signal props are removed - #948
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…rops The DIFFED hook only disposed stale updaters inside the vnode.__np branch, so a re-render that carried no signal props at all skipped disposal entirely. The orphaned updater effect kept writing the old signal's values into the DOM until unmount.
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marvinhagemeister
approved these changes
Jul 5, 2026
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Root cause
In the
DIFFEDhook, the loop that disposes updaters for props no longer bound to a signal is nested insideif (props)whereprops = vnode.__np. When a re-render passes no signal props for the element — e.g.<input value={editing ? draft : "saved"} />flipping to the plain-string branch —vnode.__npisundefinedand the whole block, including disposal, is skipped. The oldPropertyUpdatereffect stays subscribed to the previous signal and keeps writing its values straight into the DOM property, clobbering whatever Preact rendered, until the element unmounts.Fix
Run the disposal pass over
dom._updatersunconditionally, treating a missingvnode.__npthe same as "no props are signal-bound anymore", and only lazily create the updaters map when the new render actually has signal props. The regression test renders<input value={signal} />, re-renders with a plain string, then writes to the signal and asserts the DOM keeps the rendered value.Note: this PR was authored by Claude and @JoviDeCroock.