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. This is 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, and your progress syncs across the web and the CoddyKit app. The Sveltejs Academy course includes 4 lessons in total.
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.
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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. 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. The Sveltejs Academy course includes 4 lessons in total.
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, so you can start here or from the beginning and move at your own pace. This is lesson 4 of 4.
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