Top 20 Node.js Interview Questions and Answers

Node.js is a server-side JavaScript environment for developing web applications like as ASP.NET, JSP, Php etc. It is an open-source and cross-platform framework based on Google's V8 JavaScript Engine.

1. What is Node.js?

   Node.js is a server-side JavaScript environment for developing web applications like as ASP.NET, JSP, Php etc. It is an open-source and cross-platform framework based on Google's V8 JavaScript Engine.

   

   It is used to build fast and scalable network applications as well as data-intensive real-time web applications. All versions of Node.js are starting from 0.1.0 releases to 0.1.x, 0.2.x, 0.3.x, 0.4.x, 0.5.x, 0.6.x, 0.7.x, 0.8.x, 0.9.x, 0.10.x, 0.11.x, and 0.12.x. Before merging of Node.js and io.js, it’s last versions was Node.js v0.12.9.

2. What is Node.js foundation?

   The Node.js foundation is an independent foundation to take care of development and releases of Node.js. It has developers from IBM, Microsoft, PayPal, Joyent, Fidelity, SAP and other companies. On Sep 14, 2015, the Node.js foundation announced the combined release of Node.js and io.js into a single code base known as Node.js version 4.0. It has a feature of Node.js and io.js including a lot of new features of ES6.

3. What is V8 JavaScript Engine?

   V8 is an open source JavaScript engine developed by Google in 2008 to be used in Chrome browser. It is written in C++ language and implements ES5.

   

   Key Points about V8 JavaScript Engine

   • It can be run standalone or can be embedded into any C++ application.

   • It uses just-in-time compilation (JIT) to execute JavaScript code.

   • It compiles JavaScript to native machine code (IA-32, x86-64, ARM, or MIPS ISAs) before execution.

   • It is used by many open sources projects like Node.js and MongoDB to execute JavaScript on the server side.

4. What IDEs you can use for Node.js development?

   AngularJS development can be done with the help of the following IDEs:

   1. Visual Studio 2013, 2015 or higher

   2. Visual Studio Code

   3. Atom

   4. Node Eclipse

   5. WebStorm

   6. Sublime Text

5. What platforms Node.js supports?

   Node.js supports the following platforms:

   1. Linux

   2. Windows

   3. Mac OS X

   4. SunOS

6. Where you can deploy Node.js web application?

   The easiest way to deploy your Node.js web application is using Cloud server hosting like Windows Azure, Aws, Google, Heroku etc.

7. What is callback?

   A callback is a function which passed as an argument to an asynchronous function, that describes what to do after the asynchronous operation has completed. Callbacks are used frequently in node.js development.

    var fs = require('fs');
    //callback function to read file data
    fs.readFile('text.txt', 'utf8', function (err, data) { //callback function
    console.log(data);
    });
   

   What is Module?

   A module is a collection of JavaScript code which encapsulates related code into a single unit of code. Node.js has a simple module loading system. A developer can load a JavaScript library or module into his program by using the require method as given below:

    var HTTP = require('HTTP');
    

8. What is REPL Terminal?

   REPL stands for Read-Eval-Print-Loop. It is an interface to run your JavaScript code and see the results. You can access REPL by simply running a node.js command prompt and simply run the command node.

   

   Here, we are adding two numbers 1 and 2 which results into 3.

9. What is the difference between Package dependencies and development dependencies?

   Package dependencies and development dependencies, both are defined in the package.json file.

   Package Dependencies

   The dependencies field of the package.json file will have all packages listing on which your node project is dependent.

    "dependencies": {
    "angular": "1.4.8",
    "jQuery": "^2.1.4"
    }
    

   To do a listing of your node module as a dependencies package you need to use either –save flag or –production flag with node command to install package.

   Development Dependencies

   The devDependencies field of the package.json file will have those packages listing which is only required for testing and development.

    "devDependencies": {
    "mocha": " ~1.8.1"
    }
   

   To do a listing of your node module as a dependencies package you need to use –dev flag with node command to install package.

10. What are buffers?

    JavaScript language has no mechanism for reading or manipulating streams of binary data. So, Node.js introduced the Buffer class to deal with binary data. In this way, Buffer is a Node.js special data type to work with binary data. A buffer length is specified in bytes. By default, buffers are returned in data events by all Stream classes. Buffers are very fast and light objects as compared to strings. A buffer act like an array of integers, but cannot be resized.

11. What are Streams?

    Typically, Stream is a mechanism for transferring data between two points. Node.js provides you streams to read data from the source or to write data to the destination. In Node.js, Streams can be readable, writable, or both and all streams are instances of the EventEmitter class.

     var http = require('http');
     
     var server = http.createServer(function (req, res) {
     // here, req is a readable stream
     // here, res is a writable stream
     });
    

12. How to debug the code in Node.js?

    The static languages like C# and Java have tools like Visual Studio and Eclipse respectively for debugging. Node.js is based on JavaScript and in order to debug your JavaScript code we have console.log() and alert() statements. But Node.js supports other options as well for code debugging. It supports the following options:

    • The Built-In Debugger : A non-GUI tool to debug the Node.js code.

    • Node Inspector : A GUI tool to debug the Node.js code with the help of chrome or opera browser.

    • IDE Debuggers : IDE like as WebStorm, Visual Studio Code and eclipse enide etc., support the Node.js code debugging environment.

13. What are the uses of path module in Node.js?

    Node.js provides path module to normalize, join, and resolve file system paths. It also used to find relative paths, extract components from paths and determine the existence of paths.

    Note - The path module simply manipulates strings and does not interact with the file system to validate the paths.

14. What is File System module in Node.js?

    Node.js provides file system module (fs) to perform file I/O and directory I/O operations. The fs module provides both asynchronous or synchronous way to perform file I/O and directory I/O operations. The synchronous functions have “Sync” word as a suffix with their names and return the value directly. In synchronous file I/O operation, Node doesn’t execute any other code while the I/O is being performed. By default, fs module functions are asynchronous, it means they return the output of the I/O operation as a parameter to a callback function.

15. Which types of network application you can build using node.js?

    Node.js is best for developing the HTTP based application. But it is not only for developing the HTTP based application. It can be used to develop other types of applications. Like as:

    • TCP server

    • Command-line program

    • Real-time web application

    • Email server

    • File server

    • Proxy server etc.

16. What are Node.js Http module limitations?

    Node.js HTTP module has the following limitations:

    • No cookies handling or parsing.

    • No built-in session supports.

    • No built-in routing supports.

    • No static file serving.

17. What is socket.io?

    Socket.io is the most popular node.js module for WebSockets programming. It is used for two-way communication on the web. It uses events for transmitting and receiving messages between client and server.

    

    socket.emit("eventname",data) event is used for sending messages. socket.on("eventname",callback) event is used for receiving messages.

18. What are various node.js web development frameworks?

    The best and most powerful node.js web development frameworks to build real-time and scalable web applications with ease are given below:

    MVC frameworks

    • Express

    • Koa

    • Hapi

    • Sails

    • Nodal

    Full-stack frameworks

    • Meteor

    • Derby.js

    • MEAN.IO

    • MEAN.js

    • Keystone

    • Horizon

19. What are various node.js REST API frameworks?

    The best and most powerful node.js REST API frameworks to build a fast Node.js REST API server with ease are given below:

    • Restify

    • LoopBack

    • ActionHero

    • Fortune.js

Summary

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