Svelte Debugging Guide

This guide provides a systematic approach to debugging Svelte applications, with special emphasis on Svelte 5 runes and reactivity patterns.

Common Error Patterns

1. Reactivity Not Triggering

Symptoms:

• UI doesn't update when state changes
• Computed values are stale
• Event handlers seem to fire but nothing happens

Root Causes:

<!-- WRONG: Mutating object properties without reassignment (Svelte 4) -->
<script>
  let user = { name: 'John' };