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10 Important Node.js Interview Questions & Answers

April 5, 2022

What are the advanced Node.js interview questions and answers?

Node.js is a popular server-side platform used by many different organizations. If you’re preparing for a career change or have an upcoming job interview, it’s always good to prepare ahead of time and brush up on your interview skills.

In this blog post, we’ve compiled a comprehensive list of interview questions frequently encountered in Node.js interviews and the best ways to answer them.

This list of ten most advanced Node.js interview questions will help you prepare for your interview, boosting your confidence and increasing your chances of landing that Backend Developer job of your dreams!

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Best of luck with your upcoming job interview!

10 Advanced Node.js Interview Questions and Answers

1. What is REPL in Node.js?

Read-Eval-Print-Loop (REPL) is an interactive shell that processes Node.js and represents a computing environment. It’s similar to a Windows console or Unix/Linux shell where a command is entered. After that, the system responds with an output.

Read − Reads the user’s input, parses it into a JavaScript data structure, and stores it in memory.

Eval – Retrieves and evaluates the data structure.

Print – Prints the result.

Loop − Loops the above command until the user presses ctrl-c twice.


2. What is the control flow function in Node.js?

Like most languages, Node.js/JavaScript has a set of standard structured control flow structures that work like any other language.

A control flow function is a lightweight, generic piece of code that runs between several asynchronous function calls and arranges for:

  • control the execution order,
  • collect data,
  • limit concurrency and
  • call the next step in the program.

3. What is the difference between fork() and spawn() methods in Node.js?

fork() spawn()
Fork() is a specific case of spawn() that creates a new instance of a V8 engine. Spawn() starts a new process with the current instruction set.
Multiple workers work in a single node codebase for multiple tasks. This method does not create a new V8 instance and only one copy of the node module is active on the processor.


4. What is callback hell? How to avoid callback hell?

Callback hell in Node.js, also known as the pyramid of doom, is when we have complex nested callbacks. In this, each callback takes the arguments obtained as a result of previous callbacks. This kind of callback structure provides less code readability and maintainability.

With the help of Promises, we can get rid of callback hell. Promises in Javascript are a way to perform asynchronous operations in Node.js. It allows us to return a value from an asynchronous function, such as synchronous functions.


5. What is the Reactor Pattern?

The Reactor Model is used to prevent I/O operations from being blocked. This model provides a handler associated with each I/O operation.

When I/O requests are created, they are sent to a multiplexer that manages concurrency and aggregates the requests into an event and queues these events to avoid blocking the I/O mode.


6. Why does Google use V8 engine for Node.js?

V8 is the JavaScript engine that powers Google Chrome. It’s what takes the JavaScript and executes it while browsing with Chrome.

The V8 engine is open source and is written in C++ (Google Chrome uses this engine). And V8, unlike other engines, is used for the popular Node.js runtime.

Instead of using an interpreter, V8 turns JavaScript code into more efficient machine code to improve performance. It converts JavaScript code to machine code during execution using a JIT (Just In Time) compiler, as many current JavaScript engines like SpiderMonkey or Rhino (Mozilla) do.

7. What is the concept of middleware in Node.js?

Middleware is a function that receives request and response objects, just like your route handlers do.

Some of the tasks middleware functions perform are:

  • Execute any code
  • Update or replace request and response objects
  • Complete the request-response cycle
  • Call the next middleware in the stack

8. What is the purpose of NODE_ENV?

NODE_ENV is a system environment variable that Node exposes to running scripts.
The value of this type of variable can be adjusted dynamically depending on the environment the program is running on.
NODE_ENV works like a flag indicating whether the server is running in development or production mode. The express framework checks the flag value at runtime and sets the value depending on the environment.

9. What are the various timing features of Node. js ?

Timer modules in Node.js consist of functions that help control the timing of code execution. It includes the setTimeout(), setImmediate() and setInterval() methods.

  • setTimeout(): The setTimeout() method is used to schedule code execution after a specified number of milliseconds.
  • setImmediate(): The setImmediate() method is used to execute code at the end of the current event loop.
  • setInterval(): The setInterval() method is used to call a function at specified intervals (in milliseconds). Used to execute the function only once after the specified time.

10. What is WASI?

WASI is a modular system interface for WebAssembly.

WASI is being standardized in a subgroup of the WebAssembly CG.

Every WASI instance represents a unique sandbox environment. Each WASI instance must specify its command-line parameters, environment variables, and sandbox directory structure for security reasons.


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