Context API vs stores in Svelte - Interactive 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.

Trying to import 'get' as a store creator.

The writable function creates a store that can be updated and subscribed to.

2fill in blank

medium

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

Svelte

import { setContext } from 'svelte';

setContext('[1]', 42);

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

Acount

Bvalue

Ccontext

Dkey

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable named 'value' instead of a key string.

Confusing the key with the actual value.

The first argument to setContext is a key string used to identify the context value.

3fill in blank

hard

Fix the error in this Svelte code to get a context value.

Svelte

import { getContext } from 'svelte';

const value = getContext([1]);

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

A'count'

B42

Ccount

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a number or variable instead of the key string.

Forgetting to quote the key string.

The key passed to getContext must be the same string or symbol used in setContext.

4fill in blank

hard

Fill both blanks to create a derived store from a writable store.

Svelte

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

const count = writable(1);
const doubled = [2](count, n => n * 2);

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

Aderived

Bwritable

Creadable

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'writable' instead of 'derived' for computed stores.

Trying to use 'get' as a store creator.

The derived function creates a store based on other stores, here doubling the count.

5fill in blank

hard

Fill all three blanks to use a store value inside a Svelte component with reactive syntax.

Svelte

<script>
  import { [1] } from 'svelte/store';
  import { count } from './stores.js';

  $: doubled = $[2] * 2;

  function increment() {
    [3].update(n => n + 1);
  }
</script>

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

Awritable

Bcount

Dderived

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the $ prefix to access store values.

Using the wrong variable name for the store.

Import writable to create stores, use $count to access the store value reactively, and call count.update to change it.

Practice

1. Which statement best describes the main difference between Svelte's Context API and stores?

easy

A. Context API is used for styling components, stores manage component lifecycle.

B. Stores are only for passing data from parent to child, Context API is for global state.

C. Context API shares data only between parent and child components, while stores provide global reactive state accessible anywhere.

D. Stores and Context API are identical in functionality and usage.

Solution

1. Step 1: Understand Context API scope

   Context API shares data only between parent and its children components, not globally.

2. Step 2: Understand stores scope

   Stores provide reactive global state accessible from any component in the app.

3. Final Answer:

   Context API shares data only between parent and child components, while stores provide global reactive state accessible anywhere. -> Option C

4. Quick Check:

   Context API = parent-child, stores = global state [OK]

Hint: Context API is local parent-child, stores are global [OK]

Common Mistakes:

• Thinking stores only pass data down like props
• Confusing Context API with global state management
• Assuming stores are for styling or lifecycle

2. Which of the following is the correct way to set a value in a Svelte writable store?

easy

A. store.set(newValue);

B. store.value = newValue;

C. store.update(newValue);

D. store.change(newValue);

Solution

1. Step 1: Recall writable store methods

   Svelte writable stores have a set() method to assign a new value.

2. Step 2: Check other options

   store.value is not valid, update() takes a function, change() does not exist.

3. Final Answer:

   store.set(newValue); -> Option A

4. Quick Check:

   Use set() to assign store value [OK]

Hint: Use store.set(value) to update writable stores [OK]

Common Mistakes:

• Trying to assign store.value directly
• Using update() with a value instead of a function
• Using non-existent methods like change()

3. Given this Svelte code using Context API:

import { setContext, getContext } from 'svelte';

// Parent.svelte
setContext('color', 'blue');

// Child.svelte
const color = getContext('color');

What will color be inside Child.svelte?

medium

A. Throws an error

B. undefined

C. null

D. 'blue'

Solution

1. Step 1: Understand setContext and getContext

   setContext('color', 'blue') sets a value accessible to child components via getContext('color').

2. Step 2: Check child access

   Child.svelte calls getContext('color') and receives 'blue' because it is a child of the parent setting the context.

3. Final Answer:

   'blue' -> Option D

4. Quick Check:

   Context API passes 'blue' from parent to child [OK]

Hint: getContext returns parent's setContext value [OK]

Common Mistakes:

• Expecting undefined if not wrapped properly
• Confusing context keys or forgetting to setContext
• Assuming context works globally like stores

4. What is wrong with this Svelte store usage?

import { writable } from 'svelte/store';

const count = writable(0);

function increment() {
  count = count + 1;
}

medium

A. writable stores cannot hold numbers.

B. You cannot reassign the store variable; must use count.update() or count.set().

C. The import statement is incorrect.

D. The function increment should be async.

Solution

1. Step 1: Identify store usage error

   The code tries to do count = count + 1, which reassigns the store variable instead of updating its value.

2. Step 2: Correct way to update store

   Use count.update(n => n + 1) or count.set(newValue) to change the store's value reactively.

3. Final Answer:

   You cannot reassign the store variable; must use count.update() or count.set(). -> Option B

4. Quick Check:

   Update store with update() or set(), not reassignment [OK]

Hint: Use update() or set(), never reassign store variable [OK]

Common Mistakes:

• Trying to assign store variable directly
• Ignoring reactive update methods
• Thinking writable stores can't hold numbers

5. You want to share a theme color across your entire Svelte app and reactively update it from any component. Which approach is best and why?

hard

A. Use a writable store for the theme color because stores provide reactive global state accessible anywhere.

B. Use Context API because it automatically updates all components globally.

C. Pass the theme color as a prop to every component manually.

D. Use a local variable in each component to store the theme color.

Solution

1. Step 1: Identify requirement for global reactive state

   The theme color must be shared app-wide and update reactively from any component.

2. Step 2: Compare Context API and stores

   Context API only shares data between parent and children, not globally. Stores provide reactive global state accessible anywhere.

3. Final Answer:

   Use a writable store for the theme color because stores provide reactive global state accessible anywhere. -> Option A

4. Quick Check:

   Global reactive state needs stores, not Context API [OK]

Hint: Global reactive state? Use stores, not Context API [OK]

Common Mistakes:

• Choosing Context API for global state
• Passing props everywhere manually
• Using local variables that don't sync