Custom store logic in Svelte - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a custom store in Svelte?

A custom store in Svelte is a way to create your own reactive data source with custom logic for updating and subscribing, beyond the built-in writable or readable stores.

beginner

Which function do you use to create a custom store in Svelte?

You create a custom store by writing a function that returns an object with a subscribe method, and optionally set and update methods for writable behavior.

intermediate

Why would you use a custom store instead of a writable store in Svelte?

You use a custom store when you want to add extra logic like validation, side effects, or complex state management that writable stores don't support directly.

beginner

What does the subscribe method in a custom store do?

The subscribe method lets components listen to changes in the store's value and reactively update when the value changes.

intermediate

How can you add a cleanup function in a custom store?

Inside the subscribe method, you can return a function that runs when the last subscriber unsubscribes, useful for cleaning up resources like timers or event listeners.

What must a custom store in Svelte always provide?

A An update method

B A set method

C A subscribe method

D A reset method

The subscribe method is required for any Svelte store so components can listen to changes.

Which of these is NOT a reason to create a custom store?

A To automatically style components

B To share reactive state

C To add validation logic

D To handle side effects on state changes

Styling components is unrelated to store logic; stores manage data and reactivity.

How do you notify subscribers about a new value in a custom store?

A Use console.log

B Call setTimeout

C Return a cleanup function

D Call the subscriber functions with the new value

Subscribers are functions that must be called with the updated value to trigger reactive updates.

What does the cleanup function returned by subscribe do?

A Runs when the last subscriber unsubscribes

B Runs every time the value changes

C Runs before the first subscriber subscribes

D Runs when the store is created

The cleanup function is called when no subscribers remain, to free resources.

Which Svelte store type is easiest to customize with extra logic?

A Derived store

B Custom store

C Writable store

D Readable store

Custom stores let you define any logic you want, unlike built-in stores with fixed behavior.

Explain how to create a custom store in Svelte and why you might want to use one.

Think about how you share reactive data with extra control.

Describe the role of the subscribe method and the cleanup function in a custom Svelte store.

Focus on how subscriptions start and stop.