Context API vs stores in Svelte - Visual Side-by-Side Comparison

Concept Flow - Context API vs stores

Create Store

↓

Subscribe Components

↓

Update Store Value

↓

All Subscribers React

↓

Create Context

↓

Provide Context Value

↓

Consume Context in Descendants

↓

Descendants React to Changes

Shows how stores hold shared state and notify subscribers, while Context API passes data down the component tree for descendants to consume.

Execution Sample

Svelte

// Store example
import { writable } from 'svelte/store';
const count = writable(0);

// Context example
import { setContext, getContext } from 'svelte';
setContext('key', 'value');
const val = getContext('key');

This code creates a store with a number and sets a context value, showing two ways to share data in Svelte.

Execution Table

Step	Action	Store Value	Context Value	Effect on Components
1	Create store with initial value 0	0	undefined	No components subscribed yet
2	Subscribe component A to store	0	undefined	Component A will react to store changes
3	Update store value to 1	1	undefined	Component A re-renders with new value 1
4	Set context key 'key' to 'value'	1	'value'	Descendant components can access context
5	Component B calls getContext('key')	1	'value'	Component B receives 'value' from context
6	Update store value to 2	2	'value'	Component A re-renders with new value 2; context unchanged
7	No context update	2	'value'	Context consumers see same value unless context changes
8	End of trace	2	'value'	Store and context values stable

💡 Execution stops after store and context values stabilize with subscribers updated.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	Final
store (count)	0	0	0	1	2	2
context ('key')	undefined	undefined	undefined	undefined	'value'	'value'

Key Moments - 2 Insights

Why does updating the store value cause components to re-render but changing context requires explicit setContext?

Stores are reactive and notify subscribers automatically on update (see steps 3 and 6 in execution_table). Context values must be set explicitly with setContext (step 4) and only descendants that call getContext receive the value.

Can components outside the context provider access the context value?

No, only components inside the provider tree that call getContext with the matching key receive the context value (step 5). Stores can be imported anywhere and subscribed to globally.

Visual Quiz - 3 Questions

Look at the execution table, what is the store value at step 3?

A undefined

B 0

C 1

D 2

💡 Hint

Check the 'Store Value' column at step 3 in the execution_table.

At which step does the context value get set?

A Step 4

B Step 2

C Step 6

D Step 1

💡 Hint

Look for 'Set context key' action in the execution_table.

If the store value was never updated, what would happen to component A's rendering?

A It would re-render only when context changes

B It would never re-render after subscription

C It would re-render every step

D It would throw an error

💡 Hint

Refer to steps 2 and 3 in execution_table and variable_tracker for store updates.

Concept Snapshot

Svelte stores hold reactive shared state and notify all subscribers on change.
Context API passes data down the component tree for descendants to consume.
Stores can be imported and subscribed anywhere; context is scoped to descendants.
Update stores with set() or update(); setContext and getContext manage context.
Use stores for global reactive state; use context for passing data deeply without props.

Full Transcript

This visual trace compares Svelte's Context API and stores for sharing data. Stores are created with writable() and hold reactive values. Components subscribe to stores and re-render automatically when the store updates. Context API uses setContext to provide a value to descendant components, which access it with getContext. The execution table shows steps creating a store, subscribing components, updating values, setting context, and consuming context. Variable tracking shows store and context values changing over time. Key moments clarify that stores notify subscribers automatically, while context requires explicit provision and is scoped to descendants. The quiz tests understanding of store updates, context setting, and component re-rendering behavior. The snapshot summarizes when to use stores versus context in Svelte.