getContext in Svelte - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this Svelte component output when using getContext?

Consider a parent component that sets a context value and a child component that uses getContext to access it. What will the child component display?

Svelte

/* Parent.svelte */
<script>
  import Child from './Child.svelte';
  import { setContext } from 'svelte';
  setContext('color', 'blue');
</script>
<Child />

/* Child.svelte */
<script>
  import { getContext } from 'svelte';
  const color = getContext('color');
</script>
<p>The color is {color}</p>

A Runtime error: getContext called outside component

B The color is undefined

C The color is null

D The color is blue

💡 Hint

Remember that setContext shares data with child components using the same key.

The parent uses setContext('color', 'blue') to provide the value 'blue'. The child uses getContext('color') to retrieve it, so it displays 'The color is blue'.

❓ state_output

intermediate

What is the value of variable 'theme' after running this Svelte code?

Given this Svelte component code, what is the value of theme?

Svelte

<script>
  import { getContext } from 'svelte';
  const theme = getContext('theme') ?? 'light';
</script>

A undefined

B 'dark'

C 'light'

D Throws ReferenceError

💡 Hint

If no context is set for the key, the fallback value after ?? is used.

No parent component set a context for 'theme', so getContext('theme') returns undefined. The nullish coalescing operator ?? then assigns 'light'.

📝 Syntax

advanced

Which option correctly uses getContext in a Svelte component?

Choose the code snippet that correctly uses getContext to retrieve a value in a Svelte component.

A <script>import { getContext } from 'svelte'; const value = getContext('key');</script>

B <script>import { getContext } from 'svelte'; const value = getContext();</script>

C <script>import { getContext } from 'svelte'; const value = getContext(key);</script>

D <script>import { getContext } from 'svelte'; const value = getContext['key'];</script>

💡 Hint

getContext requires a string key as an argument.

Option A correctly calls getContext with a string key. Option A misses the argument, C uses an undefined variable key, and D uses incorrect syntax.

🔧 Debug

advanced

What error occurs when calling getContext with a key not set by any parent?

What happens if a Svelte component calls getContext('missingKey') but no parent component has set this context?

Svelte

<script>
  import { getContext } from 'svelte';
  const value = getContext('missingKey');
</script>

A Throws ReferenceError

B Returns undefined without error

C Throws TypeError

D Returns null

💡 Hint

Check what getContext returns if no context is found.

If no context is set for the key, getContext returns undefined silently without throwing an error.

🧠 Conceptual

expert

Why use getContext instead of props in Svelte?

Which reason best explains why a developer would use getContext instead of passing data via props?

A To share data deeply without passing props through every intermediate component

B To allow components to modify parent state directly

C To make components re-render faster by avoiding props

D To automatically bind events between components

💡 Hint

Think about how data flows through nested components.

getContext allows sharing data with deeply nested components without manually passing props through each level, simplifying code and improving maintainability.

Practice

1. What is the main purpose of getContext in Svelte?

easy

A. To access data provided by a parent component without passing props

B. To create a new reactive variable inside a component

C. To define a component's local state

D. To listen for DOM events inside a component

Solution

1. Step 1: Understand the role of getContext

   getContext is used to access data that a parent component has shared using setContext.

2. Step 2: Compare with other options

   Other options describe unrelated tasks like local state or event listening, which getContext does not do.

3. Final Answer:

   To access data provided by a parent component without passing props -> Option A

4. Quick Check:

   getContext accesses parent data = B [OK]

Hint: Remember: getContext reads shared parent data [OK]

Common Mistakes:

• Confusing getContext with local state creation
• Thinking getContext listens to events
• Assuming getContext sets data instead of getting

2. Which of the following is the correct syntax to retrieve a context value with key 'user' in a Svelte component?

easy

A. const user = getContext({ key: 'user' });

B. const user = getContext('user');

C. const user = getContext(user);

D. const user = setContext('user');

Solution

1. Step 1: Recall getContext syntax

   getContext takes a string key to retrieve the shared value.

2. Step 2: Analyze options

   const user = getContext('user'); uses the correct string key syntax. const user = setContext('user'); wrongly uses setContext. const user = getContext(user); passes a variable instead of a string. const user = getContext({ key: 'user' }); passes an object, which is invalid.

3. Final Answer:

   const user = getContext('user'); -> Option B

4. Quick Check:

   getContext('key') syntax = D [OK]

Hint: Use string keys in quotes with getContext [OK]

Common Mistakes:

• Using setContext instead of getContext
• Passing variables or objects instead of string keys
• Missing quotes around the key

3. Given the parent component sets context with setContext('theme', 'dark'), what will the child component log with console.log(getContext('theme'))?

medium

A. 'dark'

B. 'light'

C. undefined

D. null

Solution

1. Step 1: Understand setContext and getContext relation

   The parent sets the key 'theme' with value 'dark'. The child uses getContext with the same key.

2. Step 2: Determine the logged value

   Since the keys match, getContext returns 'dark'. Other options are incorrect values or undefined.

3. Final Answer:

   'dark' -> Option A

4. Quick Check:

   Matching keys return set value = A [OK]

Hint: Matching keys return parent's setContext value [OK]

Common Mistakes:

• Expecting default or unrelated values
• Using different keys causing undefined
• Confusing setContext and getContext roles

4. What is the error in this child component code snippet?

const data = getContext();

medium

A. getContext must be imported from 'svelte/store'

B. getContext cannot be used in child components

C. getContext requires two arguments

D. Missing key argument in getContext call

Solution

1. Step 1: Check getContext usage

   getContext requires a key argument to specify which context to retrieve.

2. Step 2: Evaluate the code snippet

   The snippet calls getContext without any argument, causing an error.

3. Final Answer:

   Missing key argument in getContext call -> Option D

4. Quick Check:

   getContext needs a key argument = A [OK]

Hint: Always pass a key string to getContext [OK]

Common Mistakes:

• Calling getContext without arguments
• Thinking getContext needs two arguments
• Importing getContext from wrong module

5. In a nested component structure, if a grandchild calls getContext('settings') but only the grandparent used setContext('settings', {mode: 'auto'}), what will the grandchild receive?

hard

A. An error because only the direct parent can provide context

B. undefined because context is not passed through intermediate components

C. The object {mode: 'auto'} from the grandparent

D. An empty object {} because context resets at each level

Solution

1. Step 1: Understand context propagation in Svelte

   Context set by any ancestor is accessible by all descendants, not just direct children.

2. Step 2: Apply to the nested structure

   The grandchild can access the 'settings' context set by the grandparent, receiving the object {mode: 'auto'}.

3. Final Answer:

   The object {mode: 'auto'} from the grandparent -> Option C

4. Quick Check:

   Context flows down all descendants = C [OK]

Hint: Context flows down all descendants, not just direct children [OK]

Common Mistakes:

• Thinking only direct parent context is accessible
• Expecting undefined if intermediate components don't set context
• Assuming context resets at each component level