Real-time applications are becoming standard in modern web development, and GraphQL WebSocketLink plays a key role in enabling this. Because of this, many companies ask WebSocketLink interview questions to test a candidate’s understanding of real-time data handling in GraphQL.
This post covers the most important WebSocketLink interview questions with easy-to-understand answers.
1. What Is WebSocketLink in GraphQL?
Answer:
WebSocketLink is a GraphQL link used to handle real-time communication between the client and server using WebSockets. It is mainly used for GraphQL subscriptions.
In simple terms:
WebSocketLink keeps a persistent connection open so the server can send updates to the client instantly.
2. Why Do We Need WebSocketLink in GraphQL?
Answer:
Normal GraphQL queries and mutations use HTTP, which is request–response based. This is not suitable for real-time updates.
WebSocketLink is needed because:
- HTTP connections close after one response
- Real-time data requires a continuous connection
- Subscriptions need server-to-client push
3. What Are GraphQL Subscriptions?
Answer:
Subscriptions allow clients to listen for data changes instead of requesting data repeatedly.
Examples:
- New chat message
- Live notifications
- Stock price updates
👉 Subscriptions work best with WebSocketLink.
4. How Is WebSocketLink Different from HTTPLink?
Answer:
| Feature | HTTPLink | WebSocketLink |
|---|---|---|
| Connection | One-time | Persistent |
| Real-time support | ❌ No | ✅ Yes |
| Best used for | Queries & Mutations | Subscriptions |
| Server push | ❌ No | ✅ Yes |
5. Can WebSocketLink Handle Queries and Mutations?
Answer:
Technically yes, but best practice is:
- Queries & Mutations → HTTPLink
- Subscriptions → WebSocketLink
In real projects, both links are used together using link splitting.
6. What Is Link Splitting in Apollo Client?
Answer:
Link splitting means routing GraphQL operations to different links based on their type.
Example:
- If operation is a subscription, use WebSocketLink
- Otherwise, use HTTPLink
This allows one client to support both real-time and normal requests efficiently.
7. When Should You Use WebSocketLink?
Answer:
Use WebSocketLink when your application needs:
- Real-time updates
- Instant UI refresh
- Continuous data streams
Common use cases:
- Chat applications
- Live dashboards
- Trading platforms
- Notifications systems
8. When Should You Avoid WebSocketLink?
Answer:
Avoid WebSocketLink if:
- Your app is mostly CRUD-based
- Data updates are rare
- Real-time behavior is not required
In such cases, HTTP GraphQL is sufficient.
9. How Does WebSocketLink Improve Performance?
Answer:
WebSocketLink:
- Eliminates repeated HTTP requests
- Reduces network overhead
- Pushes updates only when data changes
This leads to:
- Faster response time
- Better user experience
- Lower server load
10. How Is Authentication Handled in WebSocketLink?
Answer:
Authentication is usually handled:
- During the initial WebSocket connection
- Using headers or connection parameters (like JWT tokens)
Once authenticated, the same connection is reused for all subscriptions.
11. What Are the Challenges of Using WebSocketLink?
Answer:
Some common challenges are:
- Managing long-lived connections
- Handling reconnections
- Scaling WebSocket servers
- Security and authentication
However, these are manageable with proper architecture.
12. Is WebSocketLink Mandatory for Subscriptions?
Answer:
No, WebSocketLink is not the only option, but it is the most common and recommended approach for GraphQL subscriptions in production applications.
13. How Does WebSocketLink Work Internally?
Answer (High-level):
- Client opens a WebSocket connection
- Client subscribes to an event
- Server listens for data changes
- Server pushes updates to the client
- Client receives updates in real time
14. What Is the Role of WebSockets in GraphQL?
Answer:
WebSockets provide:
- Full-duplex communication
- Persistent connections
- Low-latency data transfer
GraphQL uses WebSockets mainly for subscriptions, and WebSocketLink acts as the bridge.
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