Readable from Writable
Expose only the read side of a writable store to consumers.
Readable from Writable is a free Sveltejs Academy lesson on CoddyKit. This is lesson 3 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.
Why Expose Read-Only
You may want internal writes but read-only access for consumers, preventing accidental mutation.
Pattern
Keep the writable private; export an object with only the subscribe method.
const _user = writable(null);
export const user = { subscribe: _user.subscribe };
export function setUser(u) { _user.set(u); }External Mutation Path
Provide explicit functions for writes. This funnels mutations through one entry point.
Combine With Methods
Often combined with the custom-store pattern: subscribe + named action methods.
Hide Implementation
Consumers do not need to know whether the source is a writable, derived, or external system.
Testing
The internal writable can be replaced for tests; consumers do not care.
Reactive Consumer
Components use $user as usual.
<p>{$user?.name}</p>TypeScript Hints
Type the exported object as Readable<T> from Svelte for clarity.
Multiple Consumers
Many components can subscribe; Svelte handles all the bookkeeping.
Pair with Validation
Validate inputs in the setter function before passing to the inner writable.
Recap Pattern Use
Use this whenever you have shared state that should only change in specific ways.
Quick Check
How do you make a readable from a writable?
Recap
Expose only subscribe from a private writable to create a read-only public store.
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Frequently Asked Questions
Is the “Readable from Writable” lesson free?
Yes — the full text of “Readable from Writable” 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 “Readable from Writable”?
Expose only the read side of a writable store to consumers. 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 3 of 4.
How long does the “Readable from Writable” 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