25 WebSockets interview questions and answers

Socket.IO Interview Questions and Answers
  • What is Socket.IO? …
  • How does the Socket.IO framework work? …
  • Can you explain what the difference between WebSockets and Ajax polling is? …
  • What are some common use cases for Socket.IO? …
  • Is it possible to run NodeJS on a browser? …
  • What do you know about of error handling in Socket.IO?

Node.js is an open-source server side runtime environment built on Chromes V8 JavaScript engine. It provides an event driven, non-blocking (asynchronous) I/O and cross-platform runtime environment for building highly scalable server-side applications using JavaScript.

Web Sockets Interview Questions and Answers

WebSocket API

establish a persistent connection between server and client

server can send message to client without being requested first.

Pros:

  • Realtime Communication: In a request-response scenario, there is no way for a server to send data to the client without having the client to request something first. A client would have to continously ask for changes in regular intervals (polling), which is not what we consider realtime.
  • Less Overhead: HTTP is a stateless protocol, thus the overhead of a HTTP header is added to every single message, which can get quite large in size. Moreover, a HTTP connection will usually only keep alive for a certain amount of requests and will be closed after some time of being idle. Thus connections will quite frequently have to be reestablished, which introduces an initial setup time due to the TCP 3-Way Handshake
  • Streaming Processing: With WebSockets one can essentially stream binary data of arbitrary size between client and server. Thus it’s well suited for stream processing tasks such as processing apps, which might stream s or video data back and forth.
  • server and client can push messages to each other at any given time.
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    Q. What is Node.js Process Model?

    Node.js runs in a single process and the application code runs in a single thread and thereby needs less resources than other platforms.

    All the user requests to your web application will be handled by a single thread and all the I/O work or long running job is performed asynchronously for a particular request. So, this single thread doesnt have to wait for the request to complete and is free to handle the next request. When asynchronous I/O work completes then it processes the request further and sends the response.

    What is Node.js good for?

    Node.js is great at handling multiple connections with low cyclomatic complexity, given that its single-threaded nature requires that we liberate the event loop as soon as possible. This makes Node.js an ideal choice for microservices and real-time applications.

    npm stands for Node.js Package Manager. It consists of a command-line interface that we can use to access an online registry of public and private packages.

    FAQ

    What is Socket.IO good for?

    Socket.IO is a library that enables low-latency, bidirectional and event-based communication between a client and a server. It is built on top of the WebSocket protocol and provides additional guarantees like fallback to HTTP long-polling or automatic reconnection.

    How many requests can Socket.IO handle?

    Once you reboot your machine, you will now be able to happily go to 55k concurrent connections (per incoming IP).

    How many rooms can Socket.IO handle?

    1 Answer. socket.io rooms are a lightweight data structure. They are simply an array of connections that are associated with that room. You can have as many as you want (within normal memory usage limits).

    Is Socket.IO difficult?

    As explained above, getting started with Socket.IO is relatively simple – all you need is a Node. js server to run it on. If you want to get started with a realtime app for a limited number of users, Socket.IO is a good option. Problems come when working at scale.

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