svelte: Allow @const inside an if block

This is supported now in 3.48.0.

Something like this (this is very similar to my use case):

<div>
  {#if selected.length == 1}
    {@const sel = selected[0]}
    <!-- some actions on this one -->
  {:else if selected.length == 0}
    none selected
  {:else}
    multiple selected
  {/if}
</div>

I arrived here from a searching for a related idea: Allowing “as” clauses on if, like with each.

It would be nice to have something like {#if expression as name}...{/if}.

This would be analogous to {#each expression as name}...{/each}.

As a workaround, can do something like: {#each f(expression) as name}...{/each} where f needs a better name and would be defined: const f = (x) => x == null ? [] : [x].

A example use for this would be something like: {#if path?.to?.container?.items as items}