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?
Answer:
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.
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Ques: 2. How can you use Timers in Node.js?
Answer:
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.
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Ques: 3. What do you mean by non-blocking mean in Node.js?
Answer:
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.
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Ques: 4. What is the main difference between Node.js and Ajex?
Answer:
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.
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Ques: 5. What are the various pros and cons of Node.js?
Answer:
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.
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Ques: 6. What is the use of method spawn() and fork()?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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.?
Answer:
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?
Answer:
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?
Answer:
These two arguments are:
a) Task function
b)
Concurrency value
Ques: 19. How to avoid Callback Hell?
Answer:
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 isNPM?
Answer:
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>
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