Context with stores in Svelte - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of setContext in Svelte?

setContext lets you share data or stores from a parent component to its children without passing props manually.

beginner

How do you access a store provided via context in a child component?

You use getContext with the same key used in setContext. Then you can subscribe or use the store directly.

intermediate

Why use context with stores instead of passing stores as props?

Context avoids prop drilling, making code cleaner and easier to maintain when many nested components need the same store.

beginner

What kind of values can be shared using Svelte's context API?

You can share any JavaScript value, including stores, functions, objects, or primitives.

intermediate

How does Svelte's context API improve component reusability?

By decoupling data sharing from component hierarchy, components can be reused without needing to pass many props explicitly.

Which Svelte function is used to provide a store to child components via context?

A setContext

B getContext

C subscribe

D writable

setContext is used to provide data or stores to child components.

How do child components access a store provided via context?

A Using <code>getContext</code>

B Using <code>setContext</code>

C Using <code>subscribe</code> only

D Passing props manually

Child components use getContext with the same key to access the store.

What problem does using context with stores solve in Svelte apps?

A Makes components class-based

B Improves CSS styling

C Avoids prop drilling

D Automatically fetches data

Context avoids prop drilling by sharing data without passing props through every level.

Can you share functions using Svelte's context API?

A No, only stores

B Yes, any JavaScript value

C Only primitives

D Only objects

Svelte's context API can share any JavaScript value, including functions.

What is required to use a store from context in a child component?

A Import the store directly

B Use <code>setContext</code> again

C Declare a new store

D Use <code>getContext</code> with the correct key

You must use getContext with the key used in setContext to access the store.

Explain how you would share a writable store from a parent to a deeply nested child component using Svelte's context API.

Think about how setContext and getContext work together with stores.

Describe the benefits of using context with stores instead of passing stores through props in Svelte.

Consider how data flows in nested components.

Practice

1. In Svelte, what is the main purpose of using setContext and getContext with stores?

easy

A. To create a new store that is only used inside one component

B. To handle HTTP requests inside components

C. To style components globally using CSS variables

D. To share reactive data easily between components without passing props through many layers

Solution

1. Step 1: Understand the role of setContext and getContext

   These functions allow sharing data between components without manually passing props down the tree.

2. Step 2: Recognize the benefit of using stores with context

   Stores provide reactive data, and context lets multiple components access the same store easily.

3. Final Answer:

   To share reactive data easily between components without passing props through many layers -> Option D

4. Quick Check:

   Context with stores = share reactive data [OK]

Hint: Context shares stores to avoid prop drilling [OK]

Common Mistakes:

• Thinking context creates new stores instead of sharing
• Confusing context with styling or HTTP handling
• Assuming context replaces all props

2. Which of the following is the correct way to provide a store via context in a Svelte parent component?

easy

A. import { getContext } from 'svelte'; getContext('key', store);

B. import { setContext } from 'svelte'; setContext('key', store);

C. import { setContext } from 'svelte'; setContext(store);

D. import { createContext } from 'svelte'; createContext('key', store);

Solution

1. Step 1: Recall the correct import and usage for setting context

   Use setContext from 'svelte' with a key and a value (store).

2. Step 2: Identify the correct syntax

   The correct call is setContext('key', store); to provide the store under a key.

3. Final Answer:

   import { setContext } from 'svelte'; setContext('key', store); -> Option B

4. Quick Check:

   setContext with key and store = import { setContext } from 'svelte'; setContext('key', store); [OK]

Hint: Use setContext with key and store in parent [OK]

Common Mistakes:

• Using getContext instead of setContext to provide
• Omitting the key argument in setContext
• Using non-existent createContext function

3. Given the following Svelte code, what will be logged to the console?

/* Parent.svelte */

medium

A. 5

B. undefined

C. Error: countStore not found

D. 0

Solution

1. Step 1: Understand the store creation and context setting

   The parent creates a writable store with initial value 5 and sets it in context under 'countStore'.

2. Step 2: Child retrieves the store and subscribes

   The child gets the store from context and subscribes to log its current value, which is 5.

3. Final Answer:

   5 -> Option A

4. Quick Check:

   Store initial value logged = 5 [OK]

Hint: Store initial value logs on subscribe [OK]

Common Mistakes:

• Expecting undefined if context key is wrong
• Confusing setContext and getContext usage
• Assuming subscription logs nothing initially

4. What is the error in this Svelte child component code that tries to get a store from context?

medium

A. Cannot subscribe to context value

B. Using getContext instead of setContext

C. Missing key argument in getContext call

D. Import statement is incorrect

Solution

1. Step 1: Check getContext usage

   getContext requires a key argument to retrieve the correct context value.

2. Step 2: Identify the missing key

   The code calls getContext() without any argument, causing an error.

3. Final Answer:

   Missing key argument in getContext call -> Option C

4. Quick Check:

   getContext needs key argument [OK]

Hint: Always pass key to getContext [OK]

Common Mistakes:

• Calling getContext without key
• Confusing getContext with setContext
• Assuming context value is not subscribable

5. You want to share a writable store with a default value of 0 across multiple nested components using context. Which approach correctly sets and uses this store so that updates in any child reflect everywhere?

hard

A. In parent: setContext('count', writable(0)); In children: const count = getContext('count'); Then use count.update() or count.set()

B. In parent: const count = writable(0); In children: import the store directly and use it

C. In parent: setContext('count', 0); In children: const count = getContext('count'); Then update count directly

D. In parent: setContext('count', writable(0)); In children: const count = getContext('count'); But children cannot update the store

Solution

1. Step 1: Provide a writable store via context in the parent

   Use setContext('count', writable(0)); to share a reactive store.

2. Step 2: Retrieve the store in children and update it

   Children get the store with getContext('count'); and can call update() or set() to change the value, reflecting everywhere.

3. Final Answer:

   In parent: setContext('count', writable(0)); In children: const count = getContext('count'); Then use count.update() or count.set() -> Option A

4. Quick Check:

   Writable store in context updates everywhere [OK]

Hint: Set writable store in context, children get and update it [OK]

Common Mistakes:

• Passing raw value instead of store in context
• Importing store directly instead of using context
• Assuming children cannot update shared store