Context vs stores decision 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'

Awritable

Breadable

Cderived

Dcontext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'readable' which is for read-only stores.

Trying to import 'context' which is not a store function.

In Svelte, writable creates a store that can be updated. This is used for reactive state.

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

Bstore

Cvalue

Dcontext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'context' as the key which is too generic.

Using 'store' which is not descriptive.

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

3fill in blank

hard

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

Svelte

import { [1] } from 'svelte';

const count = getContext('count');

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

Acontext

BsetContext

CuseContext

DgetContext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'setContext' when trying to get a value.

Using 'useContext' which is not a Svelte function.

getContext is used to retrieve a value set by setContext.

4fill in blank

hard

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

Svelte

import { writable, derived } from 'svelte/store';

const a = writable(1);
const b = writable(2);
const sum = [1]([a, b], ([$a, $b]) => $a [2] $b);

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

Aderived

B+

C-

Dwritable

Attempts:

3 left

💡 Hint

Common Mistakes

Using writable instead of derived.

Using subtraction instead of addition.

derived creates a store based on others. The function adds the two values.

5fill in blank

hard

Fill all three blanks to decide when to use context or stores in Svelte.

Svelte

/* Use context when you want to pass data [1] components without prop drilling.
   Use stores when you want [2] reactive state shared [3] many components. */

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

Abetween

Ba

Cacross

Dinside

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing 'between' and 'across' for data flow.

Using 'inside' which doesn't fit the meaning.

Context passes data between components without props.
Stores hold a reactive state shared across many components.

Practice

1. In Svelte, when should you use context instead of stores?

easy

A. To manage asynchronous data fetching

B. To share data only between a parent and its child components locally

C. To share reactive data globally across unrelated components

D. To create CSS styles scoped to a component

Solution

1. Step 1: Understand context usage

   Context is designed to share data locally down the component tree without passing props explicitly.

2. Step 2: Compare with stores

   Stores are for global reactive data accessible anywhere by importing, not limited to parent-child.

3. Final Answer:

   To share data only between a parent and its child components locally -> Option B

4. Quick Check:

   Context = local sharing [OK]

Hint: Context is for local, stores for global reactive data [OK]

Common Mistakes:

• Using stores for local-only data sharing
• Confusing context with global state management
• Thinking context is reactive globally
• Using context for styling or async tasks

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

easy

A. import { createContext } from 'svelte'; createContext('key', value);

B. import { useContext } from 'svelte'; useContext('key', value);

C. import { setContext } from 'svelte'; setContext('key', value);

D. import { setStore } from 'svelte'; setStore('key', value);

Solution

1. Step 1: Recall Svelte context API

   Svelte uses setContext to provide a value to child components.

2. Step 2: Check import and usage

   The correct import is from 'svelte' and the function is setContext with key and value.

3. Final Answer:

   import { setContext } from 'svelte'; setContext('key', value); -> Option C

4. Quick Check:

   setContext = provide context [OK]

Hint: Use setContext to provide data down the tree [OK]

Common Mistakes:

• Using createContext or useContext which are React terms
• Trying to set stores with setContext
• Wrong import paths or function names
• Confusing setContext with reactive stores

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

import { writable } from 'svelte/store';

const count = writable(0);

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

count.set(5);
count.update(n => n + 1);

medium

A. [0, 5, 6]

B. [5, 6]

C. [0, 1, 5]

D. [1, 5, 6]

Solution

1. Step 1: Understand initial subscription call

   Subscribing to a writable store immediately calls the callback with the current value, which is 0.

2. Step 2: Trace set and update calls

   Then count.set(5) triggers callback with 5, and count.update(n => n + 1) triggers callback with 6.

3. Final Answer:

   [0, 5, 6] -> Option A

4. Quick Check:

   Subscription calls on current and changes [OK]

Hint: Subscription logs current value immediately [OK]

Common Mistakes:

• Ignoring initial subscription call
• Mixing order of set and update
• Assuming update starts from 0 after set
• Confusing subscribe behavior with events

4. What is wrong with this Svelte code snippet that tries to share data using context?

import { getContext } from 'svelte';

const value = getContext('user');

console.log(value);

medium

A. It tries to get context outside a component setup, causing undefined

B. It uses getContext instead of setContext to provide data

C. The key 'user' must be an object, not a string

D. getContext requires two arguments, key and default value

Solution

1. Step 1: Check context usage location

   getContext must be called inside a component's script during initialization, not in a module scope.

2. Step 2: Understand consequence

   Calling it outside component setup returns undefined because no context is set yet.

3. Final Answer:

   It tries to get context outside a component setup, causing undefined -> Option A

4. Quick Check:

   getContext only works inside component setup [OK]

Hint: Use getContext only inside component scripts [OK]

Common Mistakes:

• Calling getContext in module scope
• Confusing getContext with setContext usage
• Assuming string keys must be objects
• Expecting getContext to have default value argument

5. You want to share a reactive theme color across many unrelated components in a Svelte app. Which approach is best and why?

hard

A. Use a global variable for shared data

B. Use context API for local tree sharing

C. Pass props through all components manually

D. Use a writable store for global reactive data

Solution

1. Step 1: Identify sharing scope

   The theme color must be shared globally across unrelated components, not just parent-child.

2. Step 2: Choose reactive global sharing

   Writable stores provide reactive global state accessible by importing anywhere.

3. Step 3: Evaluate other options

   Context is local only, props are tedious for many components, global variables lack reactivity.

4. Final Answer:

   Use a writable store for global reactive data -> Option D

5. Quick Check:

   Stores = global reactive sharing [OK]

Hint: Use stores for global reactive data, context for local only [OK]

Common Mistakes:

• Using context for global sharing
• Passing props through many unrelated components
• Using global variables without reactivity
• Ignoring reactivity needs for theme changes