Migrating from Svelte 4 to 5
Convert Svelte 4 components to runes with the official migration guide and codemods.
Migrating from Svelte 4 to 5 is a free Sveltejs Academy lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Sveltejs Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Migration Mindset
Svelte 5 is mostly backward compatible. You can migrate component-by-component.
Official Codemod
Run the migration script to convert legacy syntax automatically.
npx sv migrate svelte-5What It Does
The codemod rewrites export let to $props(), $: to $derived/$effect, etc.
Review Output
Always review the migrated code. Some patterns need manual decisions.
Coexistence
Old and new syntax can live in the same file; Svelte 5 detects per-block.
Reactive Mutations
$state proxies make array.push() reactive. You may delete old workaround reassignments.
Event Dispatcher
createEventDispatcher is replaced by callback props passed via $props().
Slots vs Snippets
Slots still work; consider rewriting to snippets for new components.
Store Compatibility
svelte/store is still supported. You can keep using stores or refactor to $state for app state.
Library Compatibility
Most libraries target both versions; update one component at a time.
Documentation
The Svelte 5 docs include a migration guide with side-by-side comparisons.
Quick Check
Can you mix Svelte 4 and 5 syntax?
Recap
Migrate to Svelte 5 with npx sv migrate svelte-5; old syntax keeps working for gradual adoption.
Frequently asked questions
Is the “Migrating from Svelte 4 to 5” lesson free?
Yes — the full text of “Migrating from Svelte 4 to 5” is free to read here on the web, and the Sveltejs Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Sveltejs Academy course, upgrade to CoddyKit PRO.
What will I learn in “Migrating from Svelte 4 to 5”?
Convert Svelte 4 components to runes with the official migration guide and codemods. You practise Sveltejs Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Sveltejs Academy?
No prior experience is required. Sveltejs Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Migrating from Svelte 4 to 5” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Sveltejs Academy lesson?
Yes. Every Sveltejs Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- $state.raw for Non-Reactive State
- $derived.by for Complex Derivations
- $effect.root for Manual Cleanup
- Migrating from Svelte 4 to 5