Context with stores in Svelte - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a writable store in Svelte.

Svelte

import { [1] } from 'svelte/store';

const count = [1](0);

Drag options to blanks, or click blank then click option'

Areadable

Bderived

Cwritable

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using readable instead of writable when you want to update the store.

Forgetting to import the store function.

The writable function creates a store you can update and subscribe to.

2fill in blank

medium

Complete the code to set a context value with a store in a Svelte component.

Svelte

import { setContext } from 'svelte';
import { writable } from 'svelte/store';

const count = writable(0);

setContext('[1]', count);

Drag options to blanks, or click blank then click option'

Acount

BstoreCount

CcontextCount

DcountStore

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name instead of a string as the context key.

Mismatching the context key between setContext and getContext.

The key used in setContext should match the name you want to identify the store by. Here, 'count' is used as the key.

3fill in blank

hard

Fix the error in the child component to get the store from context and subscribe to it.

Svelte

import { getContext } from 'svelte';

const count = getContext([1]);

count.subscribe(value => {
  console.log(value);
});

Drag options to blanks, or click blank then click option'

AcountStore

Bcount

C"count"

D'count'

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a variable instead of a string literal as the context key.

Using double quotes inconsistently.

The getContext function requires the exact string key used in setContext. It must be a string literal like 'count'.

4fill in blank

hard

Fill both blanks to create a derived store from a context store and use it in the component.

Svelte

import { getContext } from 'svelte';
import { [1] } from 'svelte/store';

const count = getContext('count');
const doubled = [2](count, $count => $count * 2);

Drag options to blanks, or click blank then click option'

Aderived

Bwritable

Creadable

Dsubscribe

Attempts:

3 left

💡 Hint

Common Mistakes

Using writable or readable instead of derived.

Not importing derived from the correct module.

The derived function creates a new store based on another store's value. You import and use derived here.

5fill in blank

hard

Fill all three blanks to update a context store value inside a component.

Svelte

import { getContext } from 'svelte';

const count = getContext('count');

function increment() {
  count.[1](n => n [2] 1);
}

<button on:click=[3]>Increment</button>

Drag options to blanks, or click blank then click option'

Aupdate

B+

Cincrement

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using set instead of update when incrementing.

Not matching the function name in the button's click handler.

The update method changes the store value based on the current value. The function increment is called on button click.

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