Mastering WebSockets: Top Interview Questions for 2024

WebSockets have become an essential technology in modern web development, enabling real-time, bidirectional communication between clients and servers. As web applications continue to evolve, the demand for efficient and responsive communication has skyrocketed. If you’re preparing for a job interview in the realm of web development, it’s crucial to be well-versed in WebSockets and related technologies.

In this article, we’ll explore some of the most frequently asked WebSockets interview questions for 2022. We’ll cover the fundamentals, advantages, comparison with other technologies, and real-world scenarios to help you ace your next interview.

1. What are WebSockets?

WebSockets are a computer communications protocol that provides a full-duplex communication channel over a single TCP connection. Unlike traditional HTTP requests, WebSockets establish a persistent connection between the client and server, allowing for real-time, bidirectional data transfer without the need for constant polling or long-polling techniques.

2. Explain Server-Sent Events (SSE) and EventSource.

Server-Sent Events (SSE) is a standard that describes how servers can initiate data transmission towards clients once an initial client connection has been established. The EventSource interface in web browsers is used to receive server-sent events from a server over HTTP.

SSE is a one-way communication channel from the server to the client, making it suitable for scenarios where the server needs to push data to the client, such as real-time updates, news feeds, or stock prices.

3. What is meant by lower latency interaction?

Lower latency interaction refers to the reduced delay in data transmission between the client and server. WebSockets provide a full-duplex communication channel, allowing for instantaneous data transfer in both directions without the overhead of HTTP request-response cycles.

This low-latency interaction is crucial for applications that require real-time updates, such as online gaming, collaborative editing tools, or chat applications, where even a slight delay can negatively impact the user experience.

4. Why use WebSockets over HTTP?

While HTTP is a reliable protocol for request-response communication, it has limitations when it comes to real-time, bidirectional data transfer. Here are some reasons why WebSockets are preferred over HTTP for certain use cases:

  • Full-duplex communication: WebSockets enable simultaneous two-way communication, allowing both the client and server to send and receive data asynchronously.
  • Lower overhead: WebSockets eliminate the need for constant HTTP headers and connection establishment, resulting in lower overhead and more efficient data transfer.
  • Real-time updates: WebSockets facilitate real-time updates and notifications without the need for polling or long-polling techniques.
  • Scalability: WebSockets are more scalable than traditional HTTP for applications with a high volume of real-time data transfer.

5. What is the difference between WebSockets and Socket.IO?

WebSockets and Socket.IO are both technologies used for real-time communication, but they differ in their approach and feature sets.

  • WebSockets: WebSockets is a protocol that provides a standardized way for bidirectional communication between the client and server over a single TCP connection. It is a low-level protocol supported natively by modern web browsers.

  • Socket.IO: Socket.IO is a library that builds upon WebSockets and provides additional features such as automatic reconnection, packet buffering, and fallback mechanisms (like long-polling) for environments that don’t support WebSockets. It aims to provide a consistent interface across different transport mechanisms.

While WebSockets is a standardized protocol, Socket.IO is a library that abstracts away the complexities of real-time communication and provides a higher-level API for developers.

6. Mention some advantages of Server-Sent Events (SSE) over WebSockets.

Although WebSockets offer bidirectional communication, Server-Sent Events (SSE) have some advantages in certain scenarios:

  • Simplicity: SSE is simpler to implement and understand, especially for scenarios where only server-to-client data transfer is required.
  • Compatibility: SSE has better browser compatibility compared to WebSockets, as it uses standard HTTP connections.
  • Connection reuse: SSE connections can be reused for different data streams, while WebSockets typically require a new connection for each stream.
  • Automatic reconnection: SSE clients automatically reconnect after a disconnection, whereas WebSockets require manual reconnection handling.

7. Explain Long Polling.

Long Polling is a technique used in web development to emulate real-time communication between the client and server. It works by establishing an HTTP connection that remains open until the server has new data to send or a timeout occurs.

When the client sends a request, the server holds the connection open until new data is available or a predetermined timeout is reached. Once the server has new data or the timeout occurs, it responds to the client with the available data or a timeout notification. The client then immediately sends a new request, and the process repeats.

Long Polling is an alternative to traditional polling, where the client repeatedly sends requests to the server at regular intervals, resulting in increased overhead and potential delays in receiving updates.

These are just a few examples of the types of WebSockets interview questions you may encounter. As you prepare, focus on understanding the fundamentals, advantages, and real-world use cases of WebSockets and related technologies. Additionally, be prepared to discuss your experience with implementing WebSockets in projects and any challenges you’ve faced or solutions you’ve developed.

Remember, the key to acing any technical interview is a solid understanding of the concepts, practical experience, and the ability to communicate your knowledge effectively. Good luck!

Web Sockets Interview Questions and Answers


What will replace WebSockets?

Improved Performance: WebTransport is a UDP-based transport protocol more performant than TCP-based protocols like WebSockets. Due to it being UDP based, there is no error correction or retransmission. Error correction refers to detecting and correcting an error that may occur in the transmitted data.

What are the challenges of WebSockets?

The main challenge is that connections to your WebSocket server need to be persistent. And even once you’ve scaled out your server nodes both vertically and horizontally, you also need to provide a solution for sharing data between the nodes.

How many connections can WebSockets handle?

How many WebSocket connections can a server handle? In theory, a server can handle up to 65,536 sockets per single IP address.

Do WebSockets use UDP or TCP?

While WebSocket works only over TCP, WebRTC is primarily used over UDP (although it can work over TCP as well). WebSocket is a better choice when data integrity is crucial, as you benefit from the underlying reliability of TCP.

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