Derived stores in Svelte - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a derived store in Svelte?

A derived store is a special store that automatically updates its value based on one or more other stores. It lets you create values that depend on other reactive data.

beginner

How do you create a derived store in Svelte?

You use the derived function from svelte/store, passing the source store(s) and a callback that returns the new value.

intermediate

Can a derived store depend on multiple stores? How?

Yes. You pass an array of stores as the first argument to derived. The callback receives their values as an array to compute the derived value.

beginner

What happens when a source store updates in a derived store?

The derived store automatically recalculates its value using the callback and updates any subscribers with the new value.

intermediate

Why use derived stores instead of manually subscribing to stores?

Derived stores simplify code by handling updates automatically and keep your reactive logic clean and declarative without manual subscriptions or updates.

Which function creates a derived store in Svelte?

A derived()

B writable()

C readable()

D subscribe()

The derived() function creates a store whose value depends on other stores.

What argument(s) does derived() take?

A No arguments

B Only a callback function

C Only one store

D One or more stores and a callback function

derived() takes one or more source stores and a callback to compute the derived value.

If a source store changes, what happens to the derived store?

A It resets to null

B It stays the same

C It recalculates and updates its value

D It unsubscribes automatically

Derived stores automatically recalculate when their source stores change.

Can a derived store be writable?

A Yes, always writable

B No, derived stores are read-only by default

C Only if created with writable()

D Only if you pass a setter function

Derived stores are read-only and update based on their source stores.

Why is using derived stores beneficial?

A They keep reactive logic clean and automatic

B They make stores writable

C They prevent updates

D They replace all stores

Derived stores help keep your code clean by automatically updating based on dependencies.

Explain how to create a derived store in Svelte and how it updates when source stores change.

Think about how derived stores react to changes in other stores.

Describe the advantages of using derived stores instead of manually subscribing to multiple stores.

Consider how derived stores simplify reactive programming.