Node.JS Interview Questions and Answers

Introduction

Nodejs is a server-side technology and is one of the most popular ones among MEAN stack developers. It is quite rewarding and popular tool that can be learned by them and this is highly in-demand by the organizations. Node.js developers are offered lucrative salaries that are around $100,000 per year. If you are also planning to shape your career as a Mean stack developer then this article will surely help you in shaping your career growth. Here, we will discuss commonly asked Node JS interview questions and answer for the mean stack developer profile.

If you want to apply as a Node.js developer then it is good to learn the basic concepts and get familiar with the language. This post will cover the questions that are mostly asked by the interviewers. The questions covered in this article will surely help you in answering most of the questions asked by the interviewer with full confidence. Moreover, here we have covered all common questions of Noed.js that are collected by the experts for fresher and experienced candidates. Both can read and practice these questions before going for an interview.

Node. JS Interview Questions And Answers

1. What is Node.js and where is it used?
2. Why should you use Node.js?
3. Enlist Node.js features.
4. How will NPM be updated to a new Node.js version?
5. Why is Node.js single threaded?
6. What is Node.js callback?
7. What is REPL and explain its role in Node.js?
8. Explain the NPM functionalities in Node.js?
9. Explain the difference between Ajax and Node.js
10. What is chaining in Node js, explain it?
11. Explain various stream of Node.js.
12. Explain and list some of the exit codes of Node.js.
13. What are Globals in Node.js?
14. How Angular JS and Node.js are different from each other?
15. How can you ensure consistent style and why is it important?
16. Explain callback hell of Node.js with an example.
17. How can you avoid callback hell?
18. Explain error-first callback.
19. Can you list on port 80 with Node, if yes then how?
20. Explain the event loops of Node.js
21. Explain test pyramid and how they can be implemented when you talk about HTTP APIs.
22. Define stub in Node.js.

Node .JS Interview Questions with Answers For Freshers

Q1). What is Node.js and where is it used?

Node.js is a server-side scripting technology that is based on JavaScript engine of Google’s V8. It is used to build scalable web application programs that are quite simple but frequently needed for application development.

I/O intensive web applications like video streaming of websites can be done through Node.js Real-time web applications can also be developed through Node.js, not only this even network applications, distributed systems, and general-purpose applications can be developed by Node.js

Q2). Why should you use Node.js?

Scalable network programs can be developed easily by Node.js and if you like to know that why we should use Node, js then due to below-listed advantages it is usually used by the organizations:

• Great concurrency is yielded by Node.js
• Every feature of Node.js is asynchronous
• It is never blocked
• It is quite faster
• A unified programming language and data type is offered by this

Q3). Enlist Node.js features.

Node.js is highly scalable and single threaded system that utilizes JavaScript as the scripting language. Rather than using separate threads or processes, it uses event-driven and asynchronous I/O. High output can also be achieved just be single threaded event loop and by its non-blocking I/O.

Q4). How will NPM be updated to a new Node.js version?

Following command is used to update NPM to a new version:

$ sudo npm install npm –g/usr/bin/npm -> /usr/lib/node_modules/npm/bin/npm-cli.js
npm@2.7.1/usr/lib/node_modules/npm

Q5). Why Node.js is single threaded?

For asynchronous processing, Node.js is single threaded technology especially for managing typical web loads, scalability, and performance. Unlike typical thread-based applications, these applications are highly optimized and have better features.

Q6). What is Node.js callback?

Call back is a Node.js function that is called when any task is completed. This function is used to avoid blocking and allows other function to run. Due to asynchronous feature, Node.js use callback function extensively. Node APIs are written to support callbacks of Node JS.

Q7). What is REPL and explain its role in Node.js?

REPL or Read Eval Print Loop are the tasks as per their names like for reading, evaluation, printing, and looping. Ad-hoc JavaScript statements are executed through REPL. It allows direct entry to the JavaScript shell prompt and the result also gets evaluated. REPL is important for testing, debugging, and experimenting.

Q8). Explain the NPM functionalities in Node.js?

NPM is Node package manager that provides below-listed two functionalities:

• js packages online repository
• Command line utility to install packages, dependency management and version management of these packages of Node.js

Q9). Explain the difference between Ajax and Node.js

Ajax is asynchronous javascript and XML and is the advance implementation of JavaScript just like Node, js. They both serve purely different purposes.

Ajax is defined and designed to update a particular section of a web page, in which user need not to update complete web page and a page section is usually updated dynamically in Ajax technology. Node.js is basically used to develop apps based on client-server architecture.

Q10). What is chaining in Node js, explain it?

When the output of one stream gets connected to another stream as input to create a chain of multiple operations then it is called chaining. It is just a mechanism to define multiple operations.

Q11). Explain various stream of Node.js

In Node.js stream allow users to read data from source and o write data to a destination in a continuous process. They are just an object and following four types of streams are there in Node.js they are:

• To provide read operation
• To provide a write operation
• To provide both read and write operation
• A duplex stream form that can perform computations as per available data.

Q12). Explain and list some of the exit codes of Node.js.

Exit codes are used to end a specific process in Node.js and are some specific codes. The processes can be any global object as well. Some of the exit codes are listed below:

• Uncaught fatal exception
• Unused
• Fatal Error
• Internal Exception handler Run-time failure
• Internal JavaScript Evaluation Failure

Q13). What are Globals in Node.js?

Globals is a group of keywords in Node JS. Below-listed keywords usually lie under this category:

• Global: Global namespace objects are represented by this and it works as a container for all other objects.
• Process: Asynchronous function can be turned to an async call back through this function. You can access it from anywhere in the code and the information of environment and application is provided by this keyword.
• Buffer: Binary data is handled by this class of Node.js

Q14). How Angular JS and Node.js are different from each other?

Angular JS framework is used for web application development while Node.js is just a runtime system that is used to develop client-server applications.

Q15). How can you ensure consistent style and why is it important?

Without adopting a new style, the team members of any project can modify a project easily. For this style generally, Standard and ESLint tools are used.f

Node. Js Interview Questions With Answers For Experienced

Q16). Explain callback hell of Node.js with an example.

A result of heavy callback nesting is known as callback hell, it makes the code highly unreadable and difficult to maintain. Like in the below listed example:

Query(“”SELECT employeeid FROM employee WHERE employeename=’Ankit’;”, function(id){ query(SELECT * FROM accounts WHERE employeeid=” + id, function(salary){ salary.each(function(sal){ query(“UPDATE salary SET value=”+(sal.value*0.1)+” WHERE id=” +sal.id,function(error){ if(!error){ console.log(“success!!”); } else console.log(“error”);} }); }); }); });

Q17). How can you avoid callback hell?

Callback hell can be avoided by following three ways:

• By using Promises
• By using yield with Generators or Promises
• Modularization: break callbacks into independent functions

Q18). Explain error-first callback.

Error-first is used to pass errors and data. if in any case when something went wrong programmers check the first argument and whereas additional arguments are used to pass data. An example is given below:

fs.readFile(filePath, function(err,data) { If(err) { });

Q19). Can you list on port 80 with Node, if yes then how?

Well, programmers must not try to listen on port 80 with Node JS, you need superuser rights to do so. This is always better to avoid this practice. But still if you want to listen this port then you can do it by running the application firstly on the port number above 1024 and then by putting Nginx like a reverse proxy.

Q20). Explain the event loops of Node.js.

Node.js runs through a single thread as per Node.js developer, but in real Node.js uses many threads through libuv. Every I/O require callbacks when you will put them into an event loop for execution. So, a chain of events is known as an event loop.

Q21). Explain test pyramid and how they can be implemented when you talk about HTTP APIs.

There must be low-level unit tests as well along with high-level unit tests as per test pyramid. For HTTP APIs it may be defined as:

• Lots of low-level unit tests for each model
• Fewer integration tests to test model interactions
• Fewer acceptance tests to test actual HTTP endpoints

Q22). Define stub in Node.js.

Stubs programs or functions are used to stimulate module or component behavior. Canned answers of the functions are provided by stubs during any test case. You can also ensure why these stubs are called.

Conclusion

Here in this blog, we have listed the most popular questions that are frequently asked by interviewers. There could be many other questions for the Node.js interview that you need to practice to clear the interview in the first attempt only. You can take the example from the internet and even add many other questions as per your experience.

The questions that are covered in the above section are collected from the persons who have attended a Node.js interview. You can also get trained by some training institute like JanBask Training that would help you in understanding concepts in depth and clear the interview in one shot only. Today, this is one of the most in-demand platforms that can help you in shaping your career as a Node.js or IT professional.