Node.js Interview Questions

Node.js Interviews are technical interviews that a company conducts to identify candidates it will hire for software development positions. In these interviews, candidates' knowledge about Node.js, their experience in application development, and their problem-solving skills are tested.

If you are going to take a Node.js Developer interview, we recommend studying the technical questions that may be asked. Therefore, we have listed the most popular Node.js interview questions and answers asked in interviews. 👇💼

 

Frequently Asked Node.js Interview Questions

1. What is Node.js?

Node.js is an open-source, cross-platform JavaScript runtime environment. The runtime internally uses Chrome V8, a JavaScript execution engine, and is also written in C++.

Server-side web applications are used to create. It is usually used for large-scale application development, especially for video streaming sites, single-page applications, and other web applications.

 

2. What architecture does Node.js use?

Node.js uses a “Single-Threaded Event Loop,” which means a single-threaded architecture. This architecture allows Node.js to use a single thread to handle multiple requests simultaneously and operate efficiently by using the event loop instead of waiting during input/output operations.

 

3. What are the differences between JavaScript and Node.js?

 

4. What are the differences between Angular and Node.js?

 

5. What is package.json?

package.json is a JSON file located in the root directory of the project. package.json contains important information about the project.

It includes readable meta data by users about the project (such as project name and description), functional meta data like package version numbers, and a list of dependencies the application requires.

package.json can be seen as follows 👇:

 

6. What is the event loop in Node.js and how does it work?

Event-driven programming is an approach that heavily uses events to trigger various functions. An event can be things like a mouse click or a key press.

 

The event loop in Node.js is one of Node.js’s most important features and handles all asynchronous callbacks in the application. Since Node.js is an event-driven language, when the application starts, the event loop also starts. This loop continuously monitors the process and waits in a loop to handle incoming events.

 

setTimeout, http.get and fs.readFile functions, each time they are called, the Node.js event loop is executed, and it proceeds with the next code without waiting for the output.

When the entire process is finished, Node.js receives the output and then executes the callback function. Therefore, all callback functions are placed in a queue in the loop. After receiving a response, they are executed one by one.

Image Source: Edureka

 

7. What is REPL in Node.js?

REPL in Node.js stands for Read Eval Print Loop. REPL is an interactive shell that processes Node.js expressions. The shell reads the JavaScript code entered by the user, evaluates the result of the code line, prints the result, and stays in the loop until the user signals to exit.

Node.js comes with a REPL environment by default. The advantage of REPL is that it allows you to quickly test JavaScript code without having to store it in a file.

💡 To start the Node.js REPL interpreter, you can type and run the “node” command in your operating system’s command interpreter.

 

8. What are REPL shortcuts? 

 

9. What is error-first callback in Node.js?

Error-first callbacks in Node.js are used to pass errors and data. They aim to make it easier to handle error scenarios when using callback functions. Callback functions are designed to pass errors and data, making it easier to handle error scenarios.

 

10. What is module.exports in Node.js?

Modules in Node.js programming are independent units of functional functionality that can be shared and reused between projects. They are used to enrich applications with functions. They also make the code more understandable by organizing and separating it.

module.exports is an object used in the module system in Node.js to determine what the module exports. In Node.js, each file is considered a module, and the module.exports object is used to share or use the contents of these modules with other modules.

 

📍 For example, below is a file named greet.js. These functions are exported using module.exports.

 

11. What is the Reactor Pattern in Node.js?

The Reactor Pattern in Node.js is a concept used to prevent blocking of I/O operations. This concept provides a handler associated with each I/O operation.

 

12. What are the security practices in Node.js?

There are essentially two security practices in Node.js:

1️⃣ Authentication: Strong authentication policies are an important defense against potential attackers.

2️⃣ Error Handling: By preparing code to handle errors, application performance and security issues can be reduced.

 

13. What are debuggers in Node.js?

Node.js inherently provides a TCP-based protocol and a debugging client.

📍 To debug a JavaScript file, use the following debugging flag and then the name of the js file you want to debug.

 

14. What is callback hell in Node.js?

✅ Callback functions mean the delayed execution of a function until another function completes its execution and returns data.

✅Callback hell in Node.js is a situation where there are numerous nested callbacks that are unreadable and cumbersome. It’s also known as the Pyramid of Doom.

✅ This situation involves multiple nested callback functions that make the code difficult to read and debug.

 

15. How to avoid callback hell in Node.js?

In Node.js, to solve this problem, the Promises method is used. 

Example syntax 👇:

 

16. What is Libuv?

Libuv is a multi-platform support library used for asynchronous I/O operations in Node.js. Although developed for Node.js, it has gradually been adopted in other systems like Luvit, pyuv, and Julia.

 

✔️ Used to manage asynchronous operations. 

✔️ Node.js’s event loop is managed by libuv. 

✔️ Used for I/O operations. 

✔️ Libuv is platform-independent. It can be used on different operating systems.

✔️ Prevents performance issues caused by CPU-intensive operations.

 

17. What is the URL module?

The URL module in Node.js is a built-in module used to parse URLs and other features. It helps break down a web address into a readable format.

👇 To include the URL module, use the require() method: 

 

18. What is the async.queue module?

In Node.js, the async.queue module is a module designed to work asynchronously with JavaScript.  The async.queue can be used by following these steps: 

1️⃣ Create a package.json file. A package.json file is created by running the “npm init” command.
2️⃣ Install the Async module by using the “npm i async” command. 

3️⃣ Import the Async module using “const async = require('async').
4️⃣ Create the async.queue module using the “const queue = async.queue('function', 'concurrency value')” syntax.

 

19. What do the spawn() and fork() methods do in Node.js?

Both spawn() and fork() methods are ways to create child processes in Node.js to reduce increasing workloads.

1️⃣ Spawn() method: The spawn() method is used to start a new process with a command line. The syntax is as follows 👇: 

 

2️⃣ fork() method: The fork() method in Node.js is a special spawn() instance that launches a new instance of the V8 engine. The syntax is as follows 👇: 

 

20. What are Node.js Global objects?

✅ Global objects in Node.js are objects that are available in all modules of the application. 

✅ Global objects can be modules, functions, and arrays. 

✅ The scope of global variables is not limited to a specific JavaScript file. They can be declared in one place and then used in multiple places.

 

21. What is a Buffer in Node.js?

Node.js Buffer is used to store raw data in a format similar to an integer array. It is a physical region of memory in the computer where data is temporarily stored while being transferred from one place to another in memory.

Some commonly used Buffer methods are 👇:

 

22. What is .env in Node.js?

NODE_ENV, indicates whether the server is running in production mode or development mode. The NODE_ENV environment variable specifies the environment in which an application is running.

NODE_ENV can be accessed like any other environment variable 👇:

 

NODE_ENV is set according to the platform used 👇: