Context vs stores decision in Svelte - Quick Revision & Key Differences

Recall & Review

beginner

What is a store in Svelte?

A store is a reactive object that holds state and allows components to subscribe to changes. It helps share data across many components easily.

beginner

What is context in Svelte used for?

Context lets a parent component pass data directly to its descendants without passing props through every level. It's good for deeply nested components.

intermediate

When should you choose stores over context in Svelte?

Use stores when you need shared state accessible by many components at different places in the app, or when state changes often and needs to be reactive.

intermediate

When is context a better choice than stores in Svelte?

Context is better when you want to pass data only to a specific subtree of components, especially if the data is static or changes rarely.

advanced

Can you combine context and stores in Svelte?

Yes! You can pass a store through context to limit its scope to a subtree, combining benefits of both patterns.

What does a Svelte store provide?

A Reactive shared state accessible by multiple components

B A way to style components globally

C A method to fetch data from APIs

D A tool to create animations

Stores hold reactive state that components can subscribe to and update.

Which Svelte feature lets a parent pass data to deeply nested children without prop drilling?

A Slots

B Stores

C Context

D Actions

Context allows passing data down the component tree without passing props at every level.

When should you prefer context over stores?

A When data needs to be shared app-wide

B When data is only needed in a specific subtree

C When you want to style components

D When you want to fetch data asynchronously

Context is ideal for passing data to a limited part of the component tree.

Can stores be passed through context in Svelte?

A Yes, to limit store scope to a subtree

B No, stores and context are incompatible

C Only if the store is writable

D Only for read-only stores

Passing stores via context scopes them to a subtree of components.

Which is NOT a benefit of using stores?

A Reactive updates across components

B Global state management

C Easy subscription and updates

D Passing data only to one child component

Stores are for shared state, not limited to a single child.

Explain when you would use context instead of stores in a Svelte app.

Think about component hierarchy and data scope.

Describe how stores and context can work together in Svelte.

Consider sharing reactive data only within part of the app.

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