Preparing for the Node js interview questions, you should start with the
basic concepts to advanced topics and move up from down. It is important to
understand how things work before moving on the more complex topics. To get the
best understanding of Node.js, you must have a basic understanding of JavaScript
related concepts as well.
Ques: 1. What can
be the possible use of DNS module in Node.js?
Ans. This is one of
the most asked Node js interview questions. The DNS module consists of an
asynchronous network wrapper. Let’s have a look at the most commonly used
functions of this module:
1.
DNS.lookup(address, options, callback) – This method takes any website’s
address as its first parameter and returns the corresponding first IPV4 or IPV6
record. The options parameter can be an integer or object. If no options are
provided both IPV4 and IPV6 are valid inputs. The third parameter is the
callback functions.
2.
DNS.lookupservice(address, port, callback) – This function converts any
physical address to an array of record types. The record types are specified by
the second parameter, rrbyte. The third method is the callback function.
3. dns.getServers()
– This function returns an array of IP address strings that are currently
configured for DNS resolution, formatted according to rfc5952. A string will
include a port section if a custom port is used.
4. DNS.setServers()
– This function sets the IP address and port of servers to be used when
performing DNS resolution. The DNS.setServers() method must not be called while
a DNS query is in progress.
Ques: 2. How can
you use Timers in Node.js?
Ans. As the name
suggests, the Timer module executes code after a set period of time. It doesn’t
need to be imported via require(). All the methods are available globally to
emulate the browser JavaScript API which provides several ways of scheduling code
to execute at a certain time.
The functions
provided by Node.js for Timers are:
setTimeout(), setImmediate(), and setInterval.
Ques: 3. What do
you mean by non-blocking mean in Node.js?
Ans. If you are talking
about non-blocking in Node.js, you are much aware about the non-blocking
I/O. It can be explained how Node uses libuv to handle its IO in a
platform-agnostic way. A non-blocking request is made and upon a request, it
queues it within the event loop. The JavaScript callback is then called on the
main JavaScript thread.
Ques: 4. What is
the main difference between Node.js and Ajax?
Ans. The easiest
way to explain the difference between Node.js and Ajax is that Node is a
server-side JavaScript, while Ajax is a client-side technology. What that means
is that Ajax is often used for updating the contents of the page without
refreshing it. Node, on the other hand, is used for developing server software,
executed by the server rather than in the browser.
Ques: 5. What are
the various pros and cons of Node.js?
Ans. Let’s take a
look at the most important pros and cons:
Pros:
- In the cases when your app doesn’t have any CPU intensive computation, you can build the whole thing in Javascript, including the basic database level. All you have to do is use JSON storage object DB like MongoDB.
- Crawlers receive a full-rendered HTML response which is great for SEO.
Cons:
- Node.js responsiveness is blocked by an intensive CPU computation so a threaded platform would a better approach in those cases.
- Using a relational database with Node.js is considered less favourable.
Ques: 6. What is the
use of method spawn() and fork()?
Ans. The spawn
method is used when a new process is to be launched with a given set of
commands. Check out the following command:
child_process.spawn(command[,
args][, options])
The fork method is
considered to be a special case for spawn() method. The following code shows
how to use it:
child_process.fork(modulePath[,
args][, options])
Ques: 7. Can you explain
the EventEmitter in Node.js?
Ans. EventMitter
class for event module helps with raising and handling custom events. You can
access it with the following code:
// Import events
module
var events =
require(‘events’);
// Create an
eventEmitter object
var eventEmitter =
new events.EventEmitter();
Ques: 8. What do you
understand by tracing?
Ans. The purpose of
tracing is to trace information generated by V8. To enable it, pass
flag-trace-events-enabled when starting the node.
All recorded
categories can be specified by the flag–trace-event categories. The enabled
logs can be opened as chrome://tracing in Chrome.
Ques:
9. Can you explain the control flow function and steps to execute it?
Ans. The control
flow function is the code that runs between asynchronous function calls.
Following steps should be followed to execute it:
- Control the order of execution.
- Collect data.
- Limit concurrency.
- Call the next step in the program.
Ques: 10. What is
the file system module of Node js?
Ans. The file
system module performs a file-related operation. It comprises synchronous and
asynchronous functions to read/write files.
For instance,
readFile() function is asynchronous function to read file content from
specified path and readFileSync() is synchronous function to read files.
Ques: 11. What are
some of the most popular modules of Node.js?
Ans. The most popular
modules Nodes.js are:
- xpress
- async
- browserify
- socket.io
- bower
- gulp
- grunt
Ques: 12. What do
you understand by package.json in node.js? What is it used for?
Ans. Package.json
holds various metadata information about the project. The information contained
in this file is then given to npm to identify the project and to handle its
dependencies.
Some of the fields
are name, description, author, and dependencies.
The dependencies
are then installed whenever the project is installed through npm. Moreover, if
the npm install is run in the root directory of the project, the dependencies
will be installed in ./node_modules directory.
Ques: 13. What is
the difference between Asynchronous and Non-blocking?
Ans. Asynchronous
or simply not synchronous means that the HTTP
requests are not waiting for the server response. You can continue with other
block and respond to the server response when received.
Non-Blocking, on
the other hand, is a term commonly used with IO. For instance, non-blocking
read/write calls return and expect the caller to call again. Read will wait
until it has some data and put calling thread to sleep.
Ques: 14. What are
the features of Node.js?
Ans. Since the APIs
of Node.js library are asynchronous, they are non-blocking which means that a
Node.js based server never waits for an API to return data. Node.js is a system
built on Google Chrome’s V8 JavaScript Engine which makes it very fast.
This system uses a
single threaded model with event looping. With the event mechanism helping the
server respond in a non-blocking way, the server is highly scalable compared to
the other servers that create limited threads to handle requests.
Ques: 15. Why should
you use Node.js?
Ans. One could use
Node.js when they want to easily build scalable apps. The biggest pros include:
- It is very fast in code execution.
- It is asynchronous and event-driven.
- It is single-threaded but highly scalable.
- No buffering.
Ques: 16. Explain
the role of REPL in Node.js.?
Ans. REPL stands
for Read, Evaluate, Print, Loop – and it performs all the mentioned tasks
accordingly. It is used to execute ad-hoc JavaScript statements and it is a
very important part of the testing and debugging process.
Ques: 17. What is libuv library? And what is its use in
Node.js?
Ans. Libuv is a
multi-platform support library with a focus on asynchronous I/O. Although it
was primarily developed for Node.js, it’s also commonly used by other systems
such as Luvit, Julia, pyuv etc.
Back in the days
when the whole Node project started, it was using Google’s V8 and Marc
Lehmann’s libev. However, the problem with libev was that it ran only on Unix
so they had to come up with the new solution to make it work on Windows,
especially once node.js grew in popularity.
Libuv was an abstraction
around libev or IOCP
depending on the platform, providing users an API based on libev. In the
node-v0.9.0 version of libuv, libev was removed.
Here are some of
the key features:
- Full-featured event loop backed by epoll, kqueue, IOCP, event ports.
- Asynchronous TCP and UDP sockets.
- Asynchronous file and file system operations.
- Child processes.
- File system events.
Ques: 18. What are
the two arguments that async.queue takes?
Ans. These two
arguments are:
a)
Task function
b)
Concurrency value
Ques: 19. How to
avoid Callback Hell?
A. Basically, every
time a long-running query finishes its execution, the callback associated with
the query is run. Since Node.js uses single thread only, it happens that it
leads to numerous queued events. And that is where the callback comes in.
There are 4 common
solutions for this issue:
Modular code – the
code split into smaller modules that are later joined together to the main
module again
Promise mechanism –
ensures either a result or error; it’s an alternative way for the async code
and it takes two optional arguments, one of which is called depending on the
state of promise
Use of generators –
they wait and resume using the yield keyword but can also suspend and resume
async operations.
Async mechanism –
the module with <async.waterfall> API which passes data from one
operation to another using the next callback.
Ques: 20. What is NPM?
A. NPM stands for
Node Package Manager. It has 2 important functions:
It works on Online
Repository for node.ls packages which are present at <nodejs.org>. In
addition to that, it also works as a command line utility and does version
management.
You can verify
version using below command: npm –version.
To install any
module you can use: npm install <Module Name>
No comments:
Post a comment