Node.JS Interview Questions and Answers

20 September, 2018


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What is node.js?

Node.js is a Server side scripting which is utilized to construct versatile projects. Its various points of interest over other server side dialects, the noticeable being non-blocking I/O.

How node.js functions?

Node.js takes a shot at a v8 domain, it is a virtual machine that uses JavaScript as its scripting dialect and accomplishes high yield by means of non-blocking I/O and single strung occasion circle.

What do you mean by the term I/O ?

I/O is the shorthand for information and yield, and it will get to anything outside of your application. It will be stacked into the machine memory to run the program, once the application is begun.

What does occasion driven programming mean?

In PC programming, occasion driven writing computer programs is a programming worldview in which the stream of the program is controlled by occasions like messages from different projects or strings. It is an application engineering procedure partitioned into two segments 1) Event Selection 2) Event Handling

Where would we be able to utilize node.js?

Node.js can be utilized for the accompanying purposes

Web applications ( particularly constant web applications )

System applications

Dispersed frameworks

Broadly useful applications

What is the upside of utilizing node.js?

It gives a simple method to manufacture versatile system programs

For the most part quick

Extraordinary simultaneousness

Nonconcurrent everything

Never pieces

What are the two sorts of API works in Node.js ?

The two sorts of API works in Node.js are

Nonconcurrent, non-blocking capacities

Synchronous, blocking capacities

What is control stream work?

A nonexclusive bit of code which keeps running in the middle of a few nonconcurrent work calls is known as control stream work.

Clarify the means how "Control Flow" controls the capacities calls?

Control the request of execution

Gather information

Breaking point simultaneousness

Call the following stage in program

Why Node.js is single strung?

For async handling, Node.js was made expressly as an investigation. It is trusted that more execution and versatility can be accomplished by doing async handling on a solitary string under normal web loads than the commonplace string based usage.

Does hub keep running on windows?

Indeed – it does. Download the MSI installer from

Would you be able to get to DOM in hub?

No, you can't get to DOM in hub.

Utilizing the occasion circle what are the assignments that ought to be done nonconcurrently?

I/O tasks

Substantial calculation

Anything requiring blocking

Why node.js is rapidly picking up consideration from JAVA developers?

Node.js is rapidly picking up consideration as it is a circle based server for JavaScript. Node.js enables client to compose the JavaScript on the server, which approaches things like HTTP stack, document I/O, TCP and databases.

What are the two contentions that async.queue takes?

The two contentions that async.queue takes

Errand work

Simultaneousness esteem

What is an occasion circle in Node.js ?

To process and handle outer occasions and to change over them into callback summons an occasion circle is utilized. In this way, at I/O calls, node.js can change starting with one demand then onto the next .

Say the means by which you can async in Node.js?

By following advances you can async Node.js

Top of the line capacities

Capacity organization

Callback Counters

Occasion circles

What are the advantages and disadvantages of Node.js?


On the off chance that your application does not have any CPU serious calculation, you can fabricate it in Javascript through and through, even down to the database level on the off chance that you utilize JSON stockpiling object DB like MongoDB.

Crawlers get a full-rendered HTML reaction, which is much more SEO neighborly as opposed to a solitary page application or a websockets application keep running over Node.js.


Any serious CPU calculation will piece node.js responsiveness, so a strung stage is a superior approach.

Utilizing social database with Node.js is viewed as less great

How Node.js defeats the issue of obstructing of I/O tasks?

Node.js takes care of this issue by putting the occasion based model at its center, utilizing an occasion circle rather than strings.

What is the contrast between Node.js versus Ajax?

The contrast amongst Node.js and Ajax is that, Ajax (short for Asynchronous Javascript and XML) is a customer side innovation, regularly utilized for refreshing the substance of the page without reviving it. While,Node.js is Server Side Javascript, utilized for creating server programming. Node.js does not execute in the program but rather by the server.

What are the Challenges with Node.js ?

Accentuating on the specialized side, it's a touch of test in Node.js to have one process with one string to scale up on multi center server.

What does it signify "non-obstructing" in node.js?

In node.js "non-blocking" implies that its IO is non-blocking.  Node utilizes "libuv" to deal with its IO in a stage freethinker way. On windows, it utilizes consummation ports for unix it utilizes epoll or kqueue and so on. Thus, it makes a non-blocking demand and upon a demand, it lines it inside the occasion circle which call the JavaScript 'callback' on the primary JavaScript string.

What is the summon that is utilized as a part of node.js to import outer libraries?

Summon "require" is utilized for bringing in outside libraries, for instance, "var http=require ("http")".  This will stack the http library and the single sent out protest through the http variable.

Say the structure most usually utilized as a part of node.js?

"Express" is the most widely recognized structure utilized as a part of node.js

What is 'Callback' in node.js?

Callback work is utilized as a part of node.js to manage different solicitations made to the server. Like on the off chance that you have a substantial record which will set aside quite a while for a server to peruse and on the off chance that you don't need a server to get take part in perusing that huge document while managing different solicitations, get back to work is utilized. Get back to work enables the server to manage pending solicitation first and call a capacity when it is done.

Learn more about Node.js Interview Questions in this blog post.

What is “callback hell” and how can it be avoided?

“Callback hell” refers to heavily nested callbacks that have become unweildy or unreadable.

An example of heavily nested code is below:


The primary method to fix callback hell is usually referred to as modularization. The callbacks are broken out into independent functions which can be called with some parameters.

How does Node.js handle child threads?

Node.js, in its essence, is a single thread process. It does not expose child threads and thread management methods to the developer. Technically, Node.js does spawn child threads for certain tasks such as asynchronous I/O, but these run behind the scenes and do not execute any application JavaScript code, nor block the main event loop.

If threading support is desired in a Node.js application, there are tools available to enable it, such as the ChildProcess module.

How does Node.js support multi-processor platforms, and does it fully utilize all processor resources?

Since Node.js is by default a single thread application, it will run on a single processor core and will not take full advantage of multiple core resources. However, Node.js provides support for deployment on multiple-core systems, to take greater advantage of the hardware. The Cluster module is one of the core Node.js modules and it allows running multiple Node.js worker processes that will share the same port.

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

Node.js core modules, as well as most of the community-published ones, follow a pattern whereby the first argument to any callback handler is an optional error object. If there is no error, the argument will be null or undefined.

A typical callback handler could therefore perform error handling as follows:


How to extract POST data in node.js?

If you use Express (High performance, high class web development for Node.js), you can do this:


<form method="post" action="/"> <input type="text" name="user[name]"> <input type="text" name="user[email]"> <input type="submit" value="Submit"> </form>


app.use(express.bodyParser();'/', function(request, response){

console.log(; console.log(;


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