Event Bus Pattern with Stores
Implement a global event bus using a writable store for decoupled communication.
Event Bus Pattern with Stores 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.
Event Bus
An event bus is a global publish/subscribe channel for decoupled communication.
Implement with writable
A writable store carrying the latest event acts as a simple bus.
const bus = writable(null);
export function emit(event) { bus.set(event); }
export function on(fn) { return bus.subscribe(e => { if (e) fn(e); }); }Use Case
One component emits a toast event; another subscribes and shows toasts globally.
Decoupling
Sender and receiver do not import each other; both depend on the bus.
Type Safety
Type events as a discriminated union for safe subscribers.
type Event = { type: "toast"; text: string } | { type: "logout" };Subscribe Once
Wrap with auto-unsubscribe via $-shorthand inside components.
Multiple Buses
Split by domain: appBus, modalBus, audioBus to avoid one giant channel.
Anti-Pattern
Overusing event buses leads to implicit data flow. Prefer direct props/stores where ownership is clear.
Replay Semantics
writable stores only hold the latest value. For full event history, use an array store.
External Events
An event bus can also wrap browser events like window resize or keyboard shortcuts.
Testing
Tests can emit events and assert subscribers respond appropriately.
Quick Check
What is the benefit of an event bus?
Recap
Build a simple event bus with a writable store. Emit and subscribe for decoupled cross-cutting communication.
Frequently asked questions
Is the “Event Bus Pattern with Stores” lesson free?
Yes — the full text of “Event Bus Pattern with Stores” 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 “Event Bus Pattern with Stores”?
Implement a global event bus using a writable store for decoupled communication. 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 “Event Bus Pattern with Stores” 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
- Store Architecture: Feature Modules
- Event Bus Pattern with Stores
- Optimistic UI Updates
- Undo/Redo with Store History