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Node.js Interview Questions and Answers | Part 2 

Pooja Goel  |   Dec 27, 2019  |  Views: 157


11. Is Node Js Single-threaded ? If yes Why?

Yes, Node.js is a Single threaded.
It has a single thread process which works on the non-blocking event loop callbacks.
We cann't create it multi-threaded.

If a request comes, it is first sent to the event queue, and executes it asynchronously, when an event is completed, another event which was passed as callback is then executed.

12. Explain callback in Node.js?

Callbacks are a normal function which is passed as a parameter to any asynchronous functions operation's completion.
It is invoked inside the another functions in which its been passed.
It's just a convention and an asynchronous equivalent for a function.
Node.js works on callbacks chain to maintain synchronization of asynchronous operations.
Due to heavy use of callbacks, there may also have callback Hell in Node.js.
Callbacks are used to write Non-Blocking Codes.

13.  For what require() is used in Node Js ?

To import the module in your application page:

cont xyz = require('module_name');

14.  What is v8 engine in node JS?

V8 is a JavaScript runtime engine built at the google development center, in Germany.
It is open source and written in C++. 
It is used for both client side (Google Chrome) and server side (node.js) JavaScript applications. 
V8 was first designed to increase the performance of the JavaScript execution inside the web browsers.

15.  Explain module.exports in Node Js ?

Node.js application is considered as a main module and a global object called module is available.
If we create our own module and want to acess globally in our all pages within the sam eapplication, we have to register our custom module inside the main module object with the help of module.exports.

const getName = () => {
  return 'DritalConnect';

module.exports.getName = getName;

16.  Which is the first argument typically passed to a Node.js callback handler ?

Error : err argument   (Follows error first concept)

17.  What are the functionalities of NPM in Node.js

To initialize the package.json file
To manage package.json file
To update npm packages
To start/build/test/debug... and noe.js application using commands

18.  What are events in Node.js?

Events are the actions, by which we can handle our callback methods synchronously.

Events can be created, fired, and listen for any action name.

Objects in Node.js also emit events which are the instances of events.EventEmitter.

fs.readStream emits an event when a file is opened.
var fs = require('fs');
var rs = fs.createReadStream('./sample.txt');
rs.on('open', function () {
  console.log('File is open');

19.  Explain event loop in Node Js ?

If a request comes, it is first sent to the event queue, and executes it asynchronously, when an event is completed, another event which was passed as callback is then executed.

20. How to create a simple server in Node js that returns Hello DritalConnect ?

Create a JavaScript file named test.js and write below code

console.log("Hello DritalConnect !!")

After creating the file, open a command prompt (cmd.exe) and run command

node test.js

Note:  test.js file path should be correctly defined., or open the cmd at the same directory the file exists.

You will see, the output "Hello DritalConnect !!" in command prompt.

Content Contributor
Pooja Goel

Pooja Goel

Sr. Software developer at Damco Solutions Pvt. Ltd.  |   Noida, Uttar Pradesh, India

I am a sr. software developer working on technologies like SQL, SSIS, SSRS, DB2,Tableau, ASP.NET having 7 years of experience.

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