Node.js is mainly a server-side scripting tool based on JavaScript and used by many developers across the globe. It is useful for creating small to enterprise-level web & mobile apps. Hence, we can say that Node.js is a go-to choice of startups, SMEs, and enterprises for making excellent applications.
If you are looking forward to hire Node.js programmer for your project but don’t know about the type of questions to ask, we’ve got your back.
eSparkBiz is a professional Node.js development services provider with years of experience in building applications using Node.js. Hence, we know what goes into hiring Node.js developer.
To begin with, a well-learned node.js developer should know all the elements of Node.js, JavaScript, HTML, CSS3, & databases like MongoDB, MYSQL, SQL, & Oracle, to be able to use them smartly. Therefore, we have compiled a list here of fundamental to advanced questions that you can ask as you interview to hire nodejs developers.
Here we go.
Technical Interview Questions to Ask While Hiring Node Developers
What is Node.js? How it is used?
Node.js is an open-source framework built on Chrome’s V8 JavaScript engine. It runs JavaScript instantly into native machine code. Enabling the web applications to run outside the client’s browser.
This lightweight framework is highly useful in building server-side applications. And also expands JavaScript API to develop standard server-side functionalities.
Apart from these, Node.js is highly useful to create data-intensive applications such as real-time apps, Network apps, etc.
What is the difference between Asynchronous & Non-Blocking?
This is the basic question to ask & get answers to as you hire dedicated node js developer.
Asynchronous in Node.js enables developers to carry out asynchronous HTTP requests without waiting for the server to respond. So the app simultaneously works on the remaining blocks and replies as soon as the server response is made.
Non-blocking functions are mostly utilized along with the I/O Operations. And these functions instantly respond with any data that is available and operate based on the requests. By chance, if any answer couldn’t be obtained, then the API responds promptly with an error.
What do you mean by the Callback function in Node.js?
Node.js is an asynchronous JavaScript framework, which depends hugely on the callbacks.
Callbacks are usually called after the completion of the assigned task. It enables the other code to execute parallelly and stop any blocking. Due to this, a Node.js application has the power to manage a wide range of I/O operations simultaneously.
What is package.json?
Package.json is a Node.js file kept at the core of the Node.js system. It is a file that holds the metadata for a specific project. Hence, the package.json file is present in the root directory of the Node application or module.
Here is how the package.json file appears instantly as soon as you create a Node.js project with the help of the command:npm init.
You can later edit the parameters as soon as you form a Node.js project.
{
“name”: “node-npm”
“version”: “1.0.0”
“description”: “A demo application”,
“main”: “index.js”,
“scripts”: {
“test”: “echo “Error:no test specified” && exit 1”
}
“author”: “Taha”,
“license”: “ISC”
}
What is Callback Hell?
Callback Hell is popularly known as the pyramid of doom. It occurs because of the actively nested, unreadable, and uncontrollable callbacks that result in difficult-to-read and debug code in the Node.js applications.
The main reason why this takes place is that developers haven’t executed asynchronous logic effectively. Also, offshore node js developers can state that this can be taken care of by using a modular process. Here, this process breaks down callbacks into separate functions that do not rely on each other.
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What are Promises?
Promises are nothing but an alternate way to write asynchronous code. Plus, they assist in managing asynchronous functions in Node.js applications.
Despite promises initially launched in the 80s, they got attention only after the evolution of JavaScript. And now, they are utilized in the latest programming languages.
In short, promises can be utilized to get an error or a result. Also, same as the classic If-else function, developers are needed to utilize the <.then> function to implement promises in a Node.js application.
What is Control Flow Function?
Anytime you write asynchronous code in Node.js, you must integrate many callback functions. If you are building a highly complex application, there is a strong possibility that you might cross the max limit of the callback function, which is 63.
After this, you will face callback hell. Hire nodejs developer who knows that one of the most effective ways to deal with this situation is to utilize the control flow function. It assists in arranging the asynchronous code by which your app doesn’t go through the callback hell.
Here are some of the things in which the control flow function can assist you:
- Fetch data
- Manage the execution order
- Integration limit
- Call the next step in the program
Lastly, you will have enhanced control over the code in your Node.js application.
Why should we use Node.js?
It is a subjective question in which the offshore node js developers can present their views about the tool and its advantages. As there are many essential advantages, a candidate can mention all the necessary things or the ones that reap the maximum benefit.
Several things that one can list about Node.js is: it is a quick, asynchronous, unified programming language and data type, etc.
In general, Node.js is a highly popular tool in the industry for developers for doing server-side development based on JavaScript.
What are Stubs?
Stubs are certain functions or programs mainly utilized for stimulating the specific module or component behavior. Also, if you hire node developers, they frequently use these in test cases because they offer answers that resolve the issues that might originate in the modules.
In short, stubs are mainly objects that keep preset data and utilize answer calls at the time of tests.
What is an Event?
The event is a primary feature of Node.js. They represent several actions that are being carried out on a web page. Moreover, they are managed by an event handler that writes the necessary code that runs the events.
What is Event-driven Programming?
Event-driven programming is a type of programming that utilizes events for activating various functions. Here events include small to big actions like a mouse click, keypress, etc.
As soon as an event gets activated, a callback function is executed that is registered with the element. This method works according to the publish-subscribe pattern. As for event-driven programming, Node.js uses it efficiently in contrast to other technologies.
What is Single-threading?
Single-threading enables developers to carry out asynchronous programming. Here, if the developer works on the standard web loads, a single thread provides higher performance and scalability as compared to typical thread-based execution.
What are worker processes?
Worker processes are mainly the processes that are executed behind when you are busy working on some other tasks. Also, they perform various activities like sending emails, fixing variables, etc. So, they are highly beneficial for developers as they finish many tedious tasks.
What is Express.js?
Even though this question is not directly linked with Node.js, it is an important question you should ask when you want to hire Node.js developer. Because a developer should know what Express.js is. As it is explicitly built for Node.js.
Notably, Express is mainly an adaptable Node.js web application framework that offers many features to create web and mobile applications.
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What is a Demultiplexer?
This is one such question that a developer, who is beginning his/her journey with Node.js might not be familiar with.
The demultiplexer is mainly a notification interface present in the JS host. It is utilized to fetch details about particular events and form quests, consequently offering the supposed Event Que.
What is REPL?
The full form of REPL is Read Evaluate Print Loop. It mainly displays a computer environment. And looks like a Windows console or Unix/Linux shell where the command is entered. This shell is widely beneficial to run specific JavaScript statements.
Does Node.js have sub-branches?
Several questions might surprise Node.js developers for hire and this question is one of them.
In case the response is NO initially, then the candidate is incorrect. Even though Node.js is a single-threaded service, it also consists of child threads. But it doesn’t showcase them to the developer.
These questions help you to identify whether the candidate has a better understanding of Node.js.
How does Node.js work?
This is something your candidate must know if you are planning to hire node js programmers for your project. First of all, the client transmits a request to the webserver to communicate with the web application. Requests are mainly blocking or non-blocking operations that include querying, updating, or deleting.
Node.js collects all the requests made by the clients & transmits them to the event loop. The event loop is mainly a functionality that looks after all the external requests & turns them into a callback function.
At the time of executing a request, Node.js links up a callback function and transfers it to the back-end. As soon as the response is available, an event is involved that activates the linked callback function to share the response.
And this is how Node.js functions.
What are the applications of Node.js?
Hire nodejs developer to build several applications on Node.js like
- I/O bound Applications
- Data Streaming Applications
- Data-intensive Real-time Applications (DIRT)
- JSON APIs-based Applications
- Complex SPAs (Single Page Applications)
- Internet of Things
- Microservices architecture
One of the most important things here is that Node.js is not proper for building complex apps that require more CPU usage.
What is NPM?
NPM is referred to as Node Package Manager. It mainly looks after various packages and modules present in Node.js.
Also, it comes with two of the most essential functionalities:
- It has an online repository for node.js packages/modules that are available inside it.
- NPM offers a command-line utility tool to install Node.js packages. And look after the version management and dependency management of Node.js packages.
Apart from NPM, there are various other packages of Node.js, which are also extensively used by the developers.
What are Modules in Node.js?
Modules in Node.js are similar to JavaScript libraries and are highly beneficial in applications to integrate a specific group of functions.
Node.js has various built-in modules which can be useful to add various primary functionalities to a web application. Here is the list of some of them:
| Primary Modules |
Description |
| HTTP |
Consists of classes, methods, and events to build a Node.js HTTP server |
| util |
Comprises utility functions beneficial for developers |
| fs |
Contains events, classes, and methods to handle file I/O operations |
| url |
Consists of various approaches for URL parsing |
| query string |
Consists of techniques to work with query string |
| stream |
Contains techniques to manage streaming data |
| zlib |
Consists of approaches to compress or decompress files |
To add a module in Node.js, take advantage of the require() function along with the parentheses that consist of the name of the module.
Which database is used with Node.js?
MongoDB is a widely used database along with Node.js. It is a NoSQL, open-source, document-oriented database that offers top-notch performance, better availability, and high flexibility.
What are some commonly used libraries in Node.js?
Hire node developers for using popular libraries in Node.js like
Express.js: Express is mainly a Node.js library available through the npm registry. It is a rapid, adaptable, and minimalistic framework that offers some essential features useful for developing web & mobile applications.
Socket.io: It is a library that offers real-time, duplex, and event-based communication between browser & server.
Mongoose: It is a Node.js web app whose core task is to attach an app to the required database.
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What are the pros and cons of Node.js?
Here are some of the most well-known pros and cons of Node.js:
| Pros |
Cons |
| Asynchronous event-driven IO supports managing multiple requests. |
Doesn’t work well with CPU-intensive tasks. |
| It utilizes JavaScript, which is quick & effective to learn. |
The callback function is problematic, as you might have to deal with some nested callbacks. |
| NPM offers extensive packages useful for an application. |
It is challenging to handle relational databases in Node.js. |
| It is highly favored for streaming large files. |
Problem with scalability. |
Which command is used to import external libraries?
To import the external commands, mainly, the required command is utilized. For instance, “var http=require (“http”)”. It will load the HTTP library along with one exported object via the HTTP variable.
What is an Event Loop in Node.js?
An event loop enables the Node.js to carry out non-blocking I/O operations, even though javascript is single-threaded. All these things can be achieved because the event loop removes procedures to the system kernel anytime possible.
What are two types of API functions in Node.js?
The main two types of API Functions available in Node.js are as follows:
- Asynchronous, non-blocking functions
- Synchronous, blocking functions
How to use URL Module in Node.js?
The URL module of Node.js offers different services for URL resolution & parsing. It consists of an inherent module that is useful in separating the web address in a readable format:
var url = require('url');
For instance:
var url = require('url');
var adrs = 'http://localhost:8082/default.htm?year=2019&month=april';
var q = url.parse(adr, true);
console.log(q.host); //returns 'localhost:8082'
console.log(q.pathname); //returns '/default.htm'
console.log(q.search); //returns '?year=2019 and month=april'
var qdata = q.query; //returns an object: { year: 2019, month: 'april' }
console.log(qdata.month); //returns 'april'
How to create a simple Express.js application?
To build a basic Express.js application, you have to follow the steps given below:
- The request object showcases an HTTP request. And consists of all the qualities of the request query string, parameters, body, HTTP headers, etc.
- The response object portrays the HTTP response, which an Express app shares when it gets an HTTP request.
What are Streams in Node.js?
Streams in Node.js are mainly a group of data that looks like arrays or strings. They are mostly objects that allow you to read data from the source and write data to require destination simultaneously. However, this data may not be displayed immediately and doesn’t have to adjust to the memory.
How to install, update & delete a dependency?
Here is the syntax you need to run to install, update, & delete a dependency respectively in Node.js.
C:Nodejs_WorkSpace>npm install express
C:Nodejs_WorkSpace>npm update express
C:Nodejs_WorkSpace>npm delete express
How to implement async in Node.js?
As represented below, the async code requests the JavaScript engine running in the code to wait for the request.get() function to finishing before shifting to the next line for execution.
async function fun1(req,rest){
let response = await request.get(‘http://localhost:3000’);
if(response.err) { console.log(‘error’);}
else { console.log(‘fetched response’);
}
What is the purpose of module.exports?
A module in Node.js is utilized to combine all the associated code into one whole unit of code. It can be read by moving all the related functions into one file. So, you can export a module with module.exports, which enables it to be imported into a different file utilizing the needed keyword.
What is the difference between Fork() & Spawn()?
Here is the difference between fork() and spawn() function:
| Fork() |
Spawn() |
| k() function is said to be the sample of the already present spawn() function. |
The Spawn() function is utilized to form a new process and launch it by accessing the processor’s node module. |
| Spawning makes sure that there are various workers on a single active worker node to manage many things simultaneously. |
It doesn’t form a new V8 instance, and just one copy of the node module is running on the processor. |
| child_process.fork(modulePath[, args][, options]) |
child_process.spawn(command[, args][, options]) |
What is Buffer Class in Node.js?
A buffer class is mainly utilized for saving the raw data in the same way, just like an array of integers. However, it matches with a raw memory allocation that is not available in the V8 heap.
Moreover, the buffer is a global class. Hence, it can be quickly accessed in various modules of the whole application. So, the Buffer class is widely utilized, as pure JavaScript is not suited for binary data.
What is Piping in Node.js?
Piping is a method utilized to join the result of one stream to another stream. It is mainly utilized to fetch data from one stream and forward it to a different stream.
What are flags used in Read/Write Operations in files?
Flags utilized for the read/write operations in files are as follows:
- r: Unlock file for reading. An exclusion happens if the file is unavailable.
- r+: Unlock file for reading and writing. An exclusion happens if the file is unavailable.
- w: Unlock the file for writing. The file is formed(if unavailable) or condensed (if already present).
- w+: Unlock file for reading and writing. The file is formed(if unavailable) and condensed (if already present).
- a: Unlock file for attaching. The file is formed if unavailable.
- a+: Unlock the file for reading and attaching. The file is formed if unavailable.
What is a Reactor Pattern in Node.js?
A reactor pattern in Node.js is mainly a theory of non-blocking I/O operations. It offers a handler that is linked with every I/O operation. When an I/O request is formed, it is sent to the demultiplexer.
The demultiplexer is an interesting notification that can manage concurrency in non-blocking I/O mode. Moreover, it supports fetching all the requests like an event and then placing every event in a line. Hence, forming a generation of the Event queues. In the same way, we desire an event loop that duplicates the events available in the event line.
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What is a Test Pyramid in Node.js?
A test pyramid is an approach used to identify the total number of test cases operated in unit testing, integration testing, and combined testing. This is retained in order to make sure that many test cases are performed for the overall development of a project.
Let’s have a brief about each of the components:
- Unit Tests: They test the overall units of the code in separation.
- Integration Tests: This test is meant for incorporating diverse units.
- End-to-end (E2E) Tests: They test the entire system, including the user interface, to data back and then reverse.
What is Middleware in Node.js?
Middleware is a practical function that possesses the capability to manage incoming requests and deliver response objects.
In short, in an app’s request-response cycle, these functions have full power over different request & response objects, including the cycle’s upcoming function. And the upcoming function of middleware is showcased using a variable, mainly named next. Some of the basic tasks that are done by the middleware functions are as follows:
- Carry out all the kinds of code
- Modify the request & response objects
- Put an end to the request & response cycle
- Call the upcoming middleware in the stack
What are different types of HTTP requests?
HTTP lists several request methods utilized to carry out certain actions. Here are some of the things done by request methods:
- GET: It is helpful to fetch the data.
- POST: Highly useful in updating a change in the state.
- HEAD: As the GET method, however, asks for the response without any need for a response body.
- DELETE: Utilized to remove any predetermined source.
How to connect MongoDB Database with Node.js?
To form a database in MongoDB:
- Begin by developing a MongoDB Client.
- Mention the connection URL, including the correct IP address and the name of the database you wish to form:
var MongoClient = require (‘mongodb’).MongoClient;
var URL = ‘mongodb://localhost:27017/mydb’;
MongoClient.connect(url, function(err,db){
if(err) throw err;
console.log(“Database Created!”);
db.close();
} );
What is the purpose of NODE_ENV?
NODE_ENV is an environmental variable that refers to the node environment present inside the express server.
When a project is in the production stage, Node.js facilitates the convention of making use of the NODE_NEW variable flag to it. This is useful in making a practical decision at the time of the development of the projects. Moreover, as soon as you keep your NODE_ENV to production, your app runs 3x speedily.
What are LTS Releases of Node.js?
LTS refers to the Long Term Support version of Node.js that gets every crucial error bug fixes, including security updates & performance improvements. These versions are supported for 1.5 years and emphasize more stability and security.
The changes carried out in the LTS versions are limited to bug fixes, security upgrades, np, documentation updates, etc.
What is Libuv?
Libuv is a multi-platform support library of Node.js that is mostly utilized for asynchronous I/O/ It was mainly built for Node.js; with passing time, it is highly used with other systems such as Luvit, pyuv, Julia, etc. Libduv is primarily an abstraction related to the libev/ IOCP based on the platform, offering users an API as per libev. Some of the essential features of the Libuv are as follows:
- Fully equipped event loop backend
- File system events
- Asynchronous file & file system operations
- Asynchronous TCP & UDP sockets
- Child processes
What is ESLint?
ESLint is an open-source project built by Nicholas C. Zakas in 2013. Its main purpose is to find a linting utility for JavaScript via a plug. Linters in Node.js are mainly useful for finding bug classes, notably those linked to a specific scope. Regulations in ESLint are highly configurable, and modified rules can be determined and loaded. It looks after the code quality and coding style problems.
Why do we use Google’s V8 Engine for Node.js?
We can use Google’s V8 Engine for Node.js as it immediately converts the JavaScript code into the native machine code. Hence, it enhances the app execution and response process and offers a high-performing app.
What do you mean by Global Objects in Node.js?
In Node.js, every object that is global in nature is termed global and is present in every module of the application. A developer can utilize these objects instantly in an app instead of planning to add them separately.
These global objects can be modules, functions, strings, objects, or anything else. Also, several objects can be in the module scope rather than the global scope.
How does Node.js handle child threads?
Node.js is a single-threaded process and no anymore discloses the child threads or thread management methods. However, you can still access the child thread by utilizing spawn () for several particular synchronous I/O tasks that run in the background. And don’t run any JS code or impede the primary event loop in the application.
In case you wish to utilize the threading idea in your app you can integrate a module known as ChildProcess.
What is Punycode in Node.js?
Punycode in Node.js is an encoding syntax that is useful for converting the Unicode (UTF-8) string of characters into the simple ASCII string of characters. It is highly essential because the hostname can decode the ASCII codes. Even though it is being utilized with various earlier versions, you can effectively use it with the following code:
punycode = require(‘punycode’);
What is the difference between Node.js and AJAX?
Before talking about the main difference between Node.js & AJAX, let’s look at what is common between them. Both Node.js and AJAX utilize the modern implementation of JavaScript.
The main dissimilarity between Node.js and AJAX is that Node.js is a server-side platform. However, AJAX is a client-side technology.
In short, Node.js helps build server-side software that is mainly performed on the servers rather than web browsers. AJAX is mainly utilized for changing the webpage contents without any need of refreshing it.
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Does Node.js provide any Debugger?
Node.js consists of an inherited TCP protocol and a debugging client. In case you have any plans to debug a file, you can utilize the debug syntax given below, followed by the js file name you want to debug.
What is Event Emitter in Node.js?
Node.js has an EventEmitter class that consists of objects that can emit events. These objects consist of an eventEmitter.on() function utilizing which various functions are associated with the event emitted by the object.
As soon as an EventEmitter class throws an event, every linked function to the particular event is called upon synchronously. Refer to the syntax given below to utilize EventEmitter in your application:
const EventEmitter = require('events');
class MyEmitter extends EventEmitter { }
const myEmitter = new MyEmitter();
myEmitter.on('event', () => {
console.log('an event occurred!');
});
myEmitter.emit('event');
Does Node.js support cryptography?
Node.js support cryptography via a special module known as Crypto. This module offers multiple cryptographic functionalities such as cipher, decipher, sign, verify, and several wrappers for SSL’s hash HMAC, etc. For reference, check the code given below:
const crypto = require'crypto');
const secret = 'akerude';
const hash = crypto.createHmac('swaEdu', secret).update('Welcome to Edureka').digest('hex');
console.log(hash);
By asking these questions to hire node.js developers, you can test their overall knowledge of Node.js. Also, it will help you make the process of hiring quick and efficient.
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