Node.js Interview Questions

1.      What is Node.js and what are its main features?

Node.js is a JavaScript runtime built on Chrome's V8 JavaScript engine. It allows developers to run JavaScript code on the server side, and enables the use of non-blocking, event-driven I/O operations.

2.      What is the difference between Node.js and JavaScript?

Node.js is a JavaScript runtime built on Chrome's V8 JavaScript engine, whereas JavaScript is a programming language that is mainly used for creating interactive front-end web applications.

3.      How does Node.js handle multiple requests?

Node.js uses an event-driven, non-blocking I/O model, which means it can handle multiple requests simultaneously by using a single thread.

4.      What is the Event loop in Node.js?

The event loop is a mechanism in Node.js that allows it to perform non-blocking I/O operations. It continuously checks the message queue for new messages, and processes them as they arrive.

5.      What is a package manager in Node.js?

A package manager is a tool that allows developers to easily manage and share third-party libraries and modules. The most commonly used package manager for Node.js is npm.

6.      What is a callback function in Node.js?

A callback function is a function that is passed as an argument to another function, and is executed after the first function has completed.

7.      What is the difference between synchronous and asynchronous code in Node.js?

Synchronous code is executed in the order it is written, whereas asynchronous code can be executed at a later time. In Node.js, asynchronous code allows for non-blocking operations and prevents the execution of the program from being blocked.

8.      What is the CommonJS module system in Node.js?

CommonJS is the module system used in Node.js, it defines a simple API for loading and working with modules, and it is designed to work in the context of a file system.

9.      What is the Express.js framework in Node.js?

Express.js is a popular web application framework for Node.js. It simplifies the process of routing, handling requests and responses, and working with middleware.

10.   What is a Stream in Node.js?

A Stream is a way to read or write data in a non-blocking way in Node.js. There are four types of streams in Node.js: readable, writable, duplex, and transform.

11.   How does Node.js handle errors?

Node.js uses the try-catch statement to handle errors, and it also has an error-first callback convention where the first argument of a callback is an error object.

12.   What is a Cluster in Node.js?

A Cluster is a way to create multiple child processes that share the same server ports, and it allows Node.js to take advantage of multiple CPUs.

13.   What is the difference between Node.js and a traditional web server?

A traditional web server serves a complete HTML page in response to a request, whereas Node.js only serves a JSON data and JavaScript code, which is then rendered by the browser.

14.   What is the process object in Node.js?

The process object is a global object that provides information about the current Node.js process and allows interaction with the process.

15.   What is a Buffer in Node.js?

A Buffer is a data structure in Node.js that stores binary data. It can be used to read and write binary data, and it allows Node.js to handle binary files.

16.   What is the difference between process.nextTick() and setImmediate() in Node.js?

process.nextTick() is a low-level function that runs the callback function immediately after the current function has completed, whereas setImmediate() runs the callback function after the current event loop.

17.   How can you debug Node.js code?

Node.js can be debugged using the built-in debugger, or by using a third-party tool like Node-Inspector or the Chrome DevTools.

18.   What is a middleware function in Node.js?

A middleware function is a function that has access to the request and response objects, and can modify or act on them before passing them to the next middleware function or the route handler.

19.   How can you secure a Node.js application?

A Node.js application can be secured by using HTTPS, validating user input, using a security middleware like helmet, rate limiting, and using a security scanner like nsp.

20.   What is a Virtual DOM in Node.js?

A Virtual DOM is a lightweight representation of the actual DOM that can be used to track changes and update the actual DOM efficiently.

21.   What is a Promises in Node.js?

Promises are a way to handle asynchronous code in Node.js. It represents a value that may not be available yet but will be at some point in the future.

22.   What is a Asynchronous Iteration in Node.js?

Asynchronous Iteration allows you to iterate over an asynchronous data source, such as a stream or a generator, in a synchronous-looking way.

23.   What is a Asynchronous Generators in Node.js?

An Asynchronous Generator is a generator that can be paused and resumed, and it can return multiple values asynchronously.

24.   What is a Asynchronous Iterator in Node.js?

An Asynchronous Iterator is an object that implements the asyncIterator interface, it allows you to iterate over an asynchronous data source.

25.   What is a Asynchronous Iterable in Node.js?

An Asynchronous Iterable is an object that implements the Symbol.asyncIterator method, it allows you to create an Asynchronous Iterator.

26.   What is the difference between fs.readFile() and fs.readFileSync() in Node.js?

fs.readFile() is an asynchronous method that reads a file and returns the contents as a buffer or a string, whereas fs.readFileSync() is a synchronous method that reads a file and returns the contents as a buffer or a string.

27.   What is the difference between fs.writeFile() and fs.writeFileSync() in Node.js?

fs.writeFile() is an asynchronous method that writes data to a file, whereas fs.writeFileSync() is a synchronous method that writes data to a file.

28.   What is the difference between require and import in Node.js?

require is the method used for loading modules in Node.js, whereas import is the method used for loading modules in the latest version of JavaScript (ES6+).

29.   What is the difference between the http and https modules in Node.js?

The http module is used for creating and handling http servers, whereas the https module is used for creating and handling https servers.

30.   What is a process object in Node.js?

The process object is a global object that provides information about the current Node.js process, and allows interaction with the process.

31.   What is the difference between a synchronous and asynchronous function in Node.js?

A synchronous function blocks the execution of the program until it returns a value, whereas an asynchronous function does not block the execution of the program and returns a promise to return a value at some point in the future.

32.   What is a buffer in Node.js?

A buffer is a container for raw binary data in Node.js, it can be used to read and write binary data.

33.   How can you handle file uploads in Node.js?

File uploads can be handled using the multer middleware which allows you to handle multipart/form-data, which is used for file uploads.

34.   What is the difference between a callback and a promise in Node.js?

A callback is a function that is passed as an argument to another function and is executed after the first function has completed, whereas a promise is an object that represents the eventual completion (or failure) of an asynchronous operation, and its resulting value.

35.   What is the purpose of the npm init command in Node.js?

The npm init command is used to create a package.json file, which contains information about the project and its dependencies.

36.   How can you test Node.js code?

Node.js code can be tested using various testing frameworks such as Mocha, Jest, or Jasmine.

37.   What is a REPL in Node.js?

REPL stands for Read-Eval-Print-Loop and it is a simple program that takes single user inputs, evaluates them, and returns the result to the user.

38.   What is a streams in Node.js?

Streams are objects that allow you to read and write data in a non-blocking way in Node.js. There are four types of streams in Node.js: readable, writable, duplex, and transform.