Custom Store Pattern with subscribe/set/update
Build a store with encapsulated logic by exposing a subscribe method and custom actions.
Custom Store Pattern with subscribe/set/update is a free Sveltejs Academy lesson on CoddyKit — lesson 2 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.
Store Contract
Any object with a subscribe(fn) method that returns an unsubscribe function is a valid Svelte store.
Wrap a writable
Build a custom store by wrapping a writable and exposing a focused API.
function createCounter() {
const { subscribe, set, update } = writable(0);
return {
subscribe,
increment: () => update(n => n + 1),
reset: () => set(0)
};
}Use It
Export an instance and consume like any store.
export const counter = createCounter();Component Use
Read with $counter, call domain methods like counter.increment().
Encapsulated Logic
Internal logic stays private; only the methods you choose are exposed.
Better Than Globals
Custom stores are testable and replaceable, unlike scattered global mutations.
Async Methods
Methods can be async and call set when ready.
load: async () => set(await fetch("/api").then(r => r.json()))Type-Safe
With TypeScript, type the return shape for full IntelliSense in consumers.
Combine with Stores
A custom store can depend on other stores internally for derived state.
Singleton vs Factory
Decide whether you want one shared instance or a factory that creates many.
Real-World Pattern
Use this for cart, auth, theme, and other domain entities in your app.
Quick Check
What makes an object a valid Svelte store?
Recap
Custom stores wrap a writable and expose domain-specific methods, keeping internal logic encapsulated.
Frequently asked questions
Is the “Custom Store Pattern with subscribe/set/update” lesson free?
Yes — the full text of “Custom Store Pattern with subscribe/set/update” 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 “Custom Store Pattern with subscribe/set/update”?
Build a store with encapsulated logic by exposing a subscribe method and custom actions. 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 2 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Custom Store Pattern with subscribe/set/update” 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
- derived() for Computed Stores
- Custom Store Pattern with subscribe/set/update
- Readable from Writable
- Store Contracts and Interoperability