Node.js Advanced Interview Questions for Experienced Professionals

Do you want to become a Node.js developer? Do you want to nail your next Node.js interview and land your dream job as a Node.js developer? If yes, keep reading.
Node.jsis an open-source, server-side implementation of the V8 JavaScript engine that is also able to run outside the browser and on other operating systems. It can be used for building fast, scalable network applications such as chat servers and crawlers that can stand up to heavy traffic volumes. The popularity of this technology continues to grow rapidly, which means there are many opportunities for those with the right skillset in this area.
If you’re working as an experienced Node js developer or any other role involving this technology, it’s important that you are armed with the necessary knowledge beforehand.

Below we have discussed some of the most common advanced interview questions related to Experienced Node.js developer roles that will help you crack your upcoming interview.

Ques 1. What is a Server Side Language?
Answer 1.A server-side language is a programming language that is used to create web applications that run on a web server. It is primarily used to process data that is sent from the client side and then send a response to the browser.

Ques 2. What is Node.js?
Answer 2. Node.js is a platform built on Chrome's JavaScript runtime that builds and runs JavaScript code outside of a browser. Node.js uses an event-driven, non-blocking I/O model that makes it lightweight and efficient for data-intensive real-time applications that run across distributed devices. It can be used to build desktop, web and mobile apps and has become increasingly popular for building newsfeeds, social media sites, chat apps and many other types of apps. Node.js can be used standalone or in conjunction with another runtime like Chromium Embedded Framework (CEF) to construct full stack web applications.

The Node.js core library provides the application programming interface (API) for building applications that use the Node.js runtime environment. The node package is the main dependency of an application written using Node.js and contains core libraries such as HTTP server and eventing modules required by all applications to function correctly.

Ques 3. Why use Node.js?
Answer 3. Node.js is a lightweight server-side JavaScript platform, which is open source and cross-platform. As a result, Node.JS can be used to build applications that can run on multiple web browsers, operating systems, and devices. In addition, Node.JS uses an event-driven architecture that makes it lightweight and highly scalable. Moreover, Node.JS offers several advantages over other technologies:

• Node.js is easy to learn and use
• Node.js allows for rapid prototyping and deployment of web applications
• Node.js is easy to debug and scale
• Node.js integrates well with legacy code
• Because of these advantages, Node.js is increasingly being adopted by organizations looking to build high-performance web applications.

Ques 4. How to write the “Hello World” program in Node.JS?
Answer 4. The first program written by every budding programmer is the ‘Hello World’ app. Let us now learn how to write this program in Node.JS. First, you need to open your code editor and create a new file. Name it as ‘hello.js’. Now write down the following code: console.log("Hello World"); If you have written the above code correctly, then it will produce the following result: Hello World

Ques 5. Which programming language to use with Node.JS?
Answer 5. You can use any programming language to integrate with Node.js. The most common ones are JavaScript, Java, Python, and Go. There are many ways to integrate code with Node.js such as npm, node-gyp, and c++ bindings. You can use any of them according to the programming language. You can also use the native bindings for specific languages. For example, to write code in Java, you can use the JVM (Java Virtual Machine) and JDK (Java Development Kit). One of the advantages of using native bindings is that they can be recompiled without having to change any code in the Node.js project.

Ques 6. What are the key elements of Node.js?
Answer 6.

• Environment: The environment in which your code is executed. It can be either the server or the client.
• Node: It is an engine for executing JavaScript outside the browser. It is a runtime built on Google’s V8 engine.
• Event Loop: A loop that listens to various events. It then performs some tasks based on the event. It can also be compared to a central processing unit (CPU).
• Callbacks: It is a function that is executed at a later time. It is a common programming pattern used in Node.js.
• Node.js: It is a JavaScript runtime built on Chrome's V8 JavaScript engine. It is a server-side framework that helps in building scalable and high-availability applications.

Ques 7. Isomorphic JavaScript: Why is it important to know?
Answer 7. Isomorphic JavaScript means that the same code can be executed both on the client and on the server. The term was coined by Facebook to describe their in-house React.js implementation. Isomorphic JavaScript is an approach to writing JavaScript applications where a single code base is shared between the client and server. This has several benefits, such Isomorphic applications are easier to scale. They can be distributed across different servers with no change to the code. This makes it easier to run on elastic cloud computing platforms like Amazon Web Services, Microsoft Azure, or Google Cloud Platform. Single code bases are easier to maintain. With one code base, one set of bugs are fixed. It is easier to write unit and integration tests.

Ques 8. What are the Advantages of Node.js?
Answer 8. The main advantage of Node.js is the ability to create scalable network applications that can take advantage of many cores and produce faster response times. Another advantage of using Node.js is the Single Codebase. You can write code for both the front-end and the back-end of your application in a single codebase. This can help you reduce the cost and time needed for development. There are also many other advantages of using Node.js. These include the fact that it is open source, has a large and active community, and is lightweight, highly scalable, and easy to use.

Ques 9. Which Languages are compatible with Node.js?
Answer 9. The following are the programming languages that are compatible with Node.js:

• JavaScript: Node.js was initially created with JavaScript and it’s the only programming language that is required to run on the server. Many users also choose Coffeescript, another version of JavaScript, instead of the standard version.
• TypeScript: is a superset of JavaScript and it can be used instead of JavaScript in a Node.js project.
• Java: Developers can use Java to write new modules or extensions for Node.js.
• Go: Go can be used to write new modules or extensions for Node.js.
• C++: Although C++ can’t be used directly, it can be used to create new modules or extensions for Node.js.

Ques 10. Which are the most common frameworks for Node.js?
Answer 10. The following are the most common frameworks for Node.js: -

• Express: It is the most popular Node.js framework, it is used for creating web applications and APIs.
• Hapi: It is another popular Node.js framework that can be used for building web applications.
• Koa: It is another open source Node.js framework created by the engineers at Airbnb.

Ques 11. What is a NPM and why does Node.js use it?
Answer 11. NPM stands for Node Package Manager. It is a package manager for JavaScript. This is not a native feature of the language but a third party tool that helps the user to install and manage the JavaScript packages. The NPM is used for dependency management and for publishing open source packages on the internet for free. Node.js uses the NPM to install and manage JavaScript packages. It is used for installing and managing third party libraries or modules. It is also used for publishing open source packages on the internet for free.

Ques 12. Why do we need Node.js in Web and Mobile apps development?

Answer 12. Many enterprise organizations are looking to build their microservices using Node.js. They want to move away from their traditional Java/PHP/Ruby stack and adopt a more contemporary approach. Node.js is great for building asynchronous, event-driven applications. It allows you to get off the single-threaded, blocking I/O model that a single language running on a single machine uses. Node.js allows you to build your services in a distributed way. You can build microservices that can run independently across multiple machines, and they can talk to each other just like they were in the same process. This allows you to build highly scalable services.

Ques 13. What is event-driven programming and why is it important?
Answer 13. Event-driven programming is an asynchronous programming style where the execution of a program is driven by external events. Events that can trigger the execution of the program include mouse clicks, text input, network requests, file system events, etc. In Node.js, the event loop is responsible for handling these events. The advantages of using event-driven programming are as follows,

• Performance : In event-driven programming, the code is executed only when an event occurs. This means that the code is executed only when necessary, so there is no need to execute it in advance. As a result, only when a certain event occurs, the code related to that event is executed. This results in lower latency and improved performance.
• Easier scalability : In event-driven programming, the program executes only when an event occurs. This makes it easier to scale the application because you can add as many instances of the program as required by keeping the program parallel and event-driven.

Ques 14. How does asynchronous programming work in node.js?
Answer 14. We have already discussed that Node.js is an asynchronous processing environment. This means that the code will not wait for the data to come. Instead, it will go ahead and execute the code and notify the data is available when it is ready. To do this, Node.js uses callbacks. A function that is executed when a particular event happens or data is read or written. A typical example would be reading data from a file. The code will not wait for the file to be read. Instead, it will read the file in the background and, when it is ready, notify the code that executed the file read operation. The code can then take the data from the callback function and use it.

Ques 15. Which tools are used for testing in node js environment?
Answer 15. There are various tools used for testing in Node.js. The most commonly used tools are JavaScript testing frameworks:

• JavaScript has many testing frameworks such as Mocha, Jasmine, and Jest. These testing tools let you write automated tests for your JavaScript code.
• JavaScript linting tools: These are used to detect errors and enforce consistent style conventions while writing JavaScript code.
• JavaScript code coverage tools: They are used to measure the coverage of your JavaScript code.

Ques 16. Does Node.js support only JSON data format?
Answer 16. No, JSON is just one of the many data types supported by Node.js, which actually offers much more. There are many different data types which are supported by Node.js such as Binary data, Text data, Globally unique identifier (GUID), International mobile equipment identifier (IMEI), JavaScript Object Notation (JSON), JavaScript Standard Library (JS), JavaScript Object Notation - External Data Representation (JSON-ER), JavaScript Object Notation - JavaScript Object Notation (JSON-JSON), JavaScript Object Notation - Binary Data (JSON-BIN), JavaScript Object Notation - Text Data (JSON-TXT), JavaScript Object Notation with Padding (JSON-P), and JavaScript Object Notation with Padding - Text Data (JSON-PTXT).

Ques 17. Is Node JS Good for HTML5 Games Development?
Answer 17. Yes, it is also used for the development of HTML5 games. Node.js is a server-side technology that can be used to build games. It is also used by many game developers to speed up the development and testing process. You can also use tools like CreateJS, Three.JS, Phaser, Pixi.JS and other tools to develop games using Node.js. You can also use Node.js to build multiplayer games, multiplayer chat, real-time game play, game chat and many other game-related features.

Ques 18. Are there any other requirements to start with Node JS development?
Answer 18. You must have a basic knowledge of JavaScript because Node.js is written using JavaScript. You should be familiar with the various features of JavaScript like syntax, variables, functions etc. You should also be comfortable with asynchronous programming, as most of the Node.js applications are built on an asynchronous design. Other programming languages that could help you strengthen your skills before you start with Node.js are Java, PHP, Python, Ruby, etc.

Ques 19. Can we run a Node.js app in the browser?
Answer 19. Yes, you can run a Node app in the browser. You just need to make sure that you use the right package for it. For example, if you want to use socket.io for real-time communication in your app, you can use websocket. Once you have the package installed, you can use the same code for the server and the browser app.

Ques 20. How to find bottlenecks in a Node JS app?
Answer 20. The first step is to monitor the application’s health by using tools like Prometheus, Grafana, and cAdvisor. You can also use the Node Inspector to debug and inspect applications and find bottlenecks in them. You should also be careful while using the console.log() function as it can slow down the application and make it prone to errors.

Ques 21. Is it true that Node.js requires more human resources compared to other frameworks?
Answer 21. It is true that Node.js requires more human resources compared to other frameworks. However, Node.js is capable of handling more traffic than other frameworks. If you are aware of Node.js and the problems it can solve, you can use it for almost anything. This means you can use it for building static websites, websites with rich interactive content, and other types of applications that can be built with it.

Ques 22. Can Node.JS be used for backend as well as frontend development?
Answer 22. Yes, you can use Node.js for both frontend and backend development. There are many frameworks that you can use with Node.js to build both the sides of the application such as Express.js, Sails.js and Hapi. The framework that you decide to use will depend on the problem that you want to solve. If you want to build a website that has a user-friendly interface, you can use a front-end framework. If you want to handle more traffic, you can use Node.js for backend development and vice versa.

Ques 23. What is an event-loop in Node JS?
Answer 23. An event loop is a mechanism that waits for an event to occur, performs the required actions, waits for other events to occur, and then repeats the process until all the events have been handled. Node JS uses an event loop to handle network I/O operations. It monitors the network socket and waits until there is data to be read or write. Once the data has been read or written, it goes back to the event loop and waits for the next event. This loop runs in a single thread and, therefore, if there is a long-running blocking operation within the event loop, the entire system freezes and no other operation can be carried out in the system. The two main events are the read and write event where the read event occurs when there is data to be read and the write event when there is data to be written. In addition to this, there are other events like DNS lookup, TCP connection, timers, and others.

Ques 24. If Node.js is single threaded then how does it handle concurrency?
Answer 24. A thread is a path of execution in a program where a set of instructions is being executed to completion. Concurrency is when many users or processes run at the same time on one machine. Single-threaded means one thread at a time. In Node.JS, there is a single thread and in this single thread, the server is run completely. This means that if there are many requests on the server, it will take the time to complete one request and then go to the next one. When it goes to the next request, it will have to wait for the previous request to finish. This is the reason why it does not have a high concurrency. However, there are many libraries that can be used for concurrency where Node.JS delegates some of the work to other threads.

Ques 25. Differentiate between process.nextTick() and setImmediate()?
Answer 25. The process.nextTick() is a function of Node.JS where it will trigger a callback after the current call finishes. For example, you have a call that will initiate a database call which will take some time to complete. You can use the next tick to initiate a call to another task which is independent of the first one. This will help in preventing the first call from being interrupted. The nextTick() function is asynchronous and it will always return the next call back. The setImmediate() is a similar approach as the nextTick() function but there is a significant difference between them. The setImmediate() will interrupt the call currently executing. This means that if you initiate a setImmediate() call in the middle of another call, it will interrupt the call and execute the call that you have set. The setImmediate() function is synchronous which means that it will wait for the call to finish before continuing with the rest of the code.

Ques 26. What are node.js streams?
Answer 26. Node.JS uses streams to read and write data from a source to a destination. This allows the application to handle large amounts of data efficiently. It also allows data from one source to be used as the input for another source. For example, you can take a connection from a database and then use it to feed a log file to the console. This makes it easier to debug the code because you can see everything in real time. You can also use streams to write to a file directly without creating a separate data stream. Streams are implemented using a few “tricks” – the data is buffered in memory and then written in one go to the destination (file or network connection). This means that a write operation cannot be interrupted and completed later (as is possible in e.g. Python). However, it is possible to pause the write operation, e.g. in order to build a progress bar or perform some other non-time-critical task.

Ques 27. What is an Event Emitter in Node.js?
Answer 27. The Event Emitter is an object that is used to trigger functions or callbacks when certain events are triggered or certain conditions are met. There are many libraries available for Event Emitters and most of the libraries that you use when you are writing Node.JS code will have an Event Emitter. An example of the Event Emitter is when you log in to any social media website, you see that the icon and the button changes when you click on it. This is done using an Event Emitter. You can write your own Event Emitter or you can use any of the readymade Event Emitters available on the internet.

Ques 28. What is a thread pool, and which Node.js library handles it?
Answer 28. A thread pool is a group of threads that can be reused for a long period of time by giving them new tasks. There are several libraries in Node.JS that use the thread pool. A few of them are: When you have to perform a CPU-intensive task, you can assign the work in a separate thread. This helps in preventing your main thread from getting blocked and the application from getting slow.

Ques 29. What is WASI and why is it being introduced?
Answer 29. The Worker-Side-ALLocated-Memory (WASI) is a new feature that is being introduced in Node.JS 12. This feature includes an additional memory segment on the main memory where the application will be able to store data so that you can perform various functions. This is an experimental feature and will be available only in the nightly version.

Ques 30. For Node.JS, why does Google use a V8 engine?
Answer 30. V8 is a JavaScript engine developed by Google and is used in Google Chrome. In order to develop Node.JS, they used V8 and that’s the reason why Node.JS uses V8 engine. The main reason for this is that V8 is a fast and efficient JavaScript engine and does not have any compilation time. It also does not have any restrictions like a JIT engine has and it can use the whole system memory. V8 is also open source and there has been a lot of work on improving it lately, especially with the introduction of Garbage Collection in the latest version.
Conclusion
The popularity of Node.js technology continues to grow rapidly, which means there are many opportunities for those with the right skillset in this area. Now that you know everything there is to know about Node.JS, you can better prepare for your next job interview.