1) What is Node.js?
Node.js is Server-side scripting which is used to build scalable programs. It is a web application framework built on Google Chrome’s JavaScript Engine. It runs within the Node.js runtime on Mac OS, Windows, and Linux with no changes. This runtime facilitates you to execute a JavaScript code on any machine outside a browser.
2) Is Node.js free to use?
Yes. It is released under MIT license and is free to use.
3) Is Node a single threaded application?
Yes. Node is a single-threaded application with event looping.
4) What are the advantages of Node.js?
Following are the main advantages of Node.js:
Node.js is asynchronous and event-driven. All API?s of Node.js library are non-blocking, and its server doesn’t wait for an API to return data. It moves to the next API after calling it, and a notification mechanism of Events of Node.js responds to the server from the previous API call.
Node.js is very fast because it builds on Google Chrome?s V8 JavaScript engine. Its library is very fast in code execution.
Node.js is single threaded but highly scalable.
Node.js provides a facility of no buffering. Its application never buffers any data. It outputs the data in chunks.
5) What is the purpose of Node.js?
These are the following purposes of Node.js:
Real-time web applications
Network applications
Distributed systems
General purpose applications
6) Explain Node.js web application architecture?
A web application distinguishes into 4 layers:
Client Layer: The Client layer contains web browsers, mobile browsers or applications which can make an HTTP request to the web server.
Server Layer: The Server layer contains the Web server which can intercept the request made by clients and pass them the response.
Business Layer: The business layer contains application server which is utilized by the web server to do required processing. This layer interacts with the data layer via database or some external programs.
Data Layer: The Data layer contains databases or any source of data.
Node.js web layer
7) What do you understand by the term I/O?
The term I/O stands for input and output. It is used to access anything outside of your application. The I/O describes any program, operation, or device that transfers data to or from a medium or another medium. This medium can be a physical device, network, or files within a system.
I/O is loaded into the machine memory to run the program once the application starts.
8) How many types of API functions are available in Node.js?
There are two types of API functions in Node.js:
Asynchronous, Non-blocking functions
Synchronous, Blocking functions
9) What do you understand by the first class function in JavaScript?
When functions are treated like any other variable, then those functions are called first-class functions. Apart from JavaScript, many other programming languages, such as Scala, Haskell, etc. follow this pattern. The first class functions can be passed as a param to another function (callback), or a function can return another function (higher-order function). Some examples of higher-order functions that are popularly used are map() and filter().
10) What is the difference between JavaScript and Node.js?
Difference between JavaScript and Node.js
The following table specifies the crucial differences between JavaScript and Node.js:
Comparison features
JavaScript
Node.js
Type
JavaScript is a programming language. More precisely, you can say that it is a scripting language used for writing scripts on the website.
Node.js is an interpreter and run time environment for JavaScript.
Utility
JavaScript is used for any client-side activity for a web application.
Node.js is used for accessing or performing any non-blocking operation of any operating system.
Running Engine
The running engine for JavaScript is Spider monkey (Firefox), JavaScript Core (Safari), V8 (Google Chrome), etc.
The running engine for Node.js is V8 (Google Chrome).
Browser compatibility
JavaScript can only be run in browsers.
The Node.js code can be run outside the browser.
Platform dependency
JavaScript is basically used on the client-side and is used in frontend development.
Node.js is mostly used on the server-side and is used in server-side development.
HTML compatibility
JavaScript is capable enough to add HTML and play with the DOM.
Node.js is not compatible enough to add HTML tags.
Examples
Some examples of the JavaScript frameworks are RamdaJS, TypedJS, etc.
Some examples of the Node.js modules are Lodash, express, etc. We have to import these modules from npm.
Written in
JavaScript is the upgraded version of ECMA script that uses Chrome’s V8 engine and is written in C++.
Node.js is written in C, C++, and Javascript.
11) Explain the working of Node.js?
The workflow of a Node.js web server typically looks like the following diagram. Let us see the flow of operations in detail:
Node.js Interview Questions
According to the above diagram, the clients send requests to the webserver to interact with the web application. These requests can be non-blocking or blocking and used for querying the data, deleting data, or updating the data.
js receives the incoming requests and adds those to the Event Queue.
After this step, the requests are passed one by one through the Event Loop. It checks if the requests are simple enough not to require any external resources.
The event loop then processes the simple requests (non-blocking operations), such as I/O Polling, and returns the responses to the corresponding clients.
A single thread from the Thread Pool is assigned to a single complex request. This thread is responsible for completing a particular blocking request by accessing external resources, such as computation, database, file system, etc.
Once the task is completed, the response is sent to the Event Loop that sends that response back to the client.
12) How can you manage the packages in your Node.js project?
We can manage the packages in our Node.js project by using several package installers and their configuration file accordingly. Most of them use npm or yarn. The npm and yarn both provide almost all libraries of JavaScript with extended features of controlling environment-specific configurations. We can use package.json and package-lock.json to maintain versions of libs being installed in a project. So, there is no issue in porting that app to a different environment.
13) Why is Node.js Single-threaded?
Node.js is a single-threaded application with event looping for async processing. The biggest advantage of doing async processing on a single thread under typical web loads is that you can achieve more performance and scalability than the typical thread-based implementation.
14) What do you understand by callback hell in Node.js?
Callback hell is a phenomenon that creates a lot of problems for a JavaScript developer when he tries to execute multiple asynchronous operations one after the other. A function is called an asynchronous function when some external activity must complete before processing a result. It is called asynchronous because there is an unpredictable amount of time before a result becomes available. These functions require a callback function to handle errors and process the result.
Example:
getData(function(a){
getMoreData(a, function(b){
getMoreData(b, function(c){
getMoreData(c, function(d){
getMoreData(d, function(e){
…
});
});
});
});
});
15) How is Node.js better than other most popular frameworks?
Based on the following criteria, we can say that Node.js is better than other most popular frameworks:
js makes development simple because of its non-blocking I/O and even-based model. This simplicity results in short response time and concurrent processing, unlike other frameworks where developers use thread management.
js runs on a chrome V8 engine which is written in C++. It enhances its performance highly with constant improvement.
With Node.js, we will use JavaScript in both the frontend and backend development that will be much faster.
js provides ample libraries so that we don’t need to reinvent the wheel.
16) In which types of applications is Node.js most frequently used?
Node.js is most frequently and widely used in the following applications:
Internet of Things
Real-time collaboration tools
Real-time chats
Complex SPAs (Single-Page Applications)
Streaming applications
Microservices architecture etc.
17) What are some commonly used timing features of Node.js?
Following is a list of some commonly used timing features of Node.js:
setTimeout/clearTimeout: This timing feature of Node.js is used to implement delays in the code execution.
setInterval/clearInterval: The setInterval or clearInterval timing feature is used to run a code block multiple times in the application.
setImmediate/clearImmediate: This timing feature of Node.js is used to set the execution of the code at the end of the event loop cycle.
nextTick: This timing feature sets the execution of code at the beginning of the next event loop cycle.
18) What do you understand by the term fork in Node.js?
Generally, a fork is used to spawn child processes. In Node.js, it is used to create a new instance of the V8 engine to run multiple workers to execute the code.
19) Which is the best tool we can use to assure consistent code style in Node.js?
ESLint tool is one of the best tools we can use with any IDE to ensure a consistent coding style. It also helps in maintaining the codebase.
20) What is the main difference between front-end and back-end development?
The following table specifies the key differences between a front-end and back-end development:
Front-end Development
Back-end Development
The front-end development in an application refers to the client-side of an application.
The back-end development in an application refers to the server-side of an application.
As the name specifies, the front-end development is the part of a web application where users can see and interact.
As the name specifies, the back-end development consists of everything that happens behind the scenes and users cannot see and interact with.
The front-end development includes everything that attributes to the visual aspects of a web application.
The back-end development generally includes a web server that communicates with the database to serve the users’ requests.
HTML, CSS, Bootstrap, jQuery, JavaScript, AngularJS, and React.js are essential front-end development technologies.
Java, PHP, Python, C++, Node.js, etc., are the technologies required for back-end development.
Examples of some front-end frameworks are AngularJS, React.js, jQuery, Sass, etc.
Examples of some back-end frameworks are Express, Django, Rails, Laravel, Spring, etc.
21) Give an example to demonstrate how can we use async await in Node.js?
See the following example of using async-await pattern:
function wait (timeout) {
return new Promise((resolve) => {
setTimeout(() => {
resolve()
}, timeout);
});
}
async function requestWithRetry (url) {
const MAX_RETRIES = 10;
for (let i = 0; i <= MAX_RETRIES; i++) {
try {
return await request(url);
} catch (err) {
const timeout = Math.pow(2, i);
console.log(‘Waiting’, timeout, ‘ms’);
await wait(timeout);
console.log(‘Retrying’, err.message, i);
}
}
}
22) What are the modules in Node.js? Which are the different modules used in Node.js?
In Node.js applications, modules are like JavaScript libraries and include a set of functions. To include a module in a Node.js application, we must use the require() function with the parentheses containing the module’s name.
Node.js has several modules which are used to provide the basic functionality needed for a web application. Following is a list of some of them:
Core Modules
Description
HTTP:
The HTTP module includes classes, methods, and events to create a Node.js HTTP server.
util:
The util module includes utility functions required in the application and is very useful for developers.
url:
The url module is used to include the methods for URL parsing.
fs:
The fs module includes events, classes, and methods to handle the file I/O operations.
stream:
The stream module is used to include the methods to handle streaming data.
query string:
The query string module is used to include the methods to work with a query string.
zlib:
The zlib module is used to include the methods to compress or decompress the files used in an application.
23) What is error-first callback?
Error-first callbacks are used to pass errors and data. If something goes wrong, the programmer has to check the first argument because it is always an error argument. Additional arguments are used to pass data.
fs.readFile(filePath, function(err, data) {
if (err) {
//handle the error
}
// use the data object
});
4) What are buffers in Node.js?
In general, a buffer is a temporary memory mainly used by the stream to hold on to some data until it is consumed. Buffers are used to represent a fixed-size chunk of memory allocated outside of the V8 JavaScript engine. It can’t be resized. It is like an array of integers, which each represents a byte of data. It is implemented by the Node. js Buffer class. Buffers also support legacy encodings like ASCII, utf-8, etc.
25) What is an asynchronous API?
All the API’s of Node.js library are asynchronous means non-blocking. A Node.js based server never waits for an API to return data. The Node.js server moves to the next API after calling it, and a notification mechanism of Events of Node.js responds to the server for the previous API call.
26) Does Node.js provide Debugger?
Yes, Node.js provides a simple TCP based protocol and built-in debugging client. For debugging your JavaScript file, you can use debug argument followed by the js file name you want to debug.
Syntax:
node debug [script.js | -e “script” | :]
27) How can you avoid callbacks?
To avoid callbacks, you can use any one of the following options:
You can use modularization. It breaks callbacks into independent functions.
You can use promises.
You can use yield with Generators and Promises.
28) What is a control flow function?
Control flow function is a generic piece of code that runs in between several asynchronous function calls.
29) How “Control Flow” controls the functions calls?
The control flow does the following job:
Control the order of execution
Collect data
Limit concurrency
Call the next step in a program
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