Svelte不更新一个if分支中的值

<script>
  import { reactive } from 'svelte';

  let showBranchA = true;
  let showBranchB = false;

  const reactiveValue = reactive(() => {
    if (showBranchA) {
      return 'Value in Branch A';
    } else if (showBranchB) {
      return 'Value in Branch B';
    } else {
      return 'Default Value';
    }
  });

  function updateValue() {
    showBranchA = !showBranchA;
    showBranchB = !showBranchB;
  }
</script>

<button on:click={updateValue}>Toggle Branch</button>

{#if showBranchA}
  <p>{reactiveValue}</p>
{/if}

{#if showBranchB}
  <p>{reactiveValue}</p>
{/if}