Unwrap signals returned from Show's when callback - #975
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When when is a function like () => someSignal, Show used the returned Signal
object directly in its truthiness check. Signal objects are always truthy, so
the fallback branch was never shown — even when the signal's value was falsy.
Show now unwraps the return value when it is a Signal, reading .value before
the truthiness check. This matches the existing behavior for the non-callback
form (when={someSignal}), which already reads .value.
Assisted-By: devx/dca78f42-f55f-4065-b66c-fc3731bd0420
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Size Change: +10 B (+0.01%) Total Size: 199 kB 📦 View Changed
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| typeof props.when === "function" ? props.when() : props.when.value; | ||
| // Unwrap a signal returned by a `when` callback so `when={() => someSignal}` | ||
| // checks the signal's value, not the signal object (which is always truthy). | ||
| const value = |
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I am not a big fan of this, this feels like just adding bytes. The callback was intended to be a shortcut to a computed
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fair point, I'll move that to the SFC compiler
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Problem
When
Show'swhenprop is a callback like() => someSignal, the returned Signal object was used directly in the truthiness check. Since Signal objects are always truthy, the fallback branch was never rendered — even when the signal's value wasfalse,0, ``, ornull.This is inconsistent with the non-callback form
when={someSignal}, which already reads.value.Fix
Unwrap the return value when it's a Signal, reading
.valuebefore the truthiness check:Why this matters
SFC compilers (like
@preact-labs/sfc-codegen) emit{#if expr}blocks as<Show when={() => expr}>. Whenexpris a signal, the callback returns the Signal object. Without unwrapping,{#if falsySignal}would always render the consequent branch instead of the fallback.