DEV Community: Dev Raj Sharma

Crack the JavaScript Interview: 20 Core Concepts Explained Like a Chat Over Coffee

Dev Raj Sharma — Tue, 15 Sep 2026 08:19:56 +0000

Skip the dry documentation. Here is your friendly, bite-sized guide to passing your next frontend interview without stress.
If you've been interviewing for frontend developer roles lately, you know the drill. You spent years building polished user interfaces and shipping clean code, but suddenly you're asked to explain prototype chains or microtask priority off the top of your head.
Instead of reading formal documentation filled with dense academic phrasing, let's go through the 20 most essential JavaScript interview questions in simple, plain language.

What's the difference between var, let, and const? Think of var as the old-school way we used to declare variables. It's function-scoped and gets hoisted (meaning JS moves the declaration to the top). The problem? It lets you re-declare variables in the same scope, leading to weird bugs. let and const were introduced in ES6: let is block-scoped (lives inside {}) and allows re-assignment.

const is also block-scoped, but once assigned, you can't re-assign it. (Note: Object properties inside a const can still be updated!)

How does Hoisting actually work? JavaScript reads your code twice before running it. In the first pass, it takes variable and function declarations and conceptually moves them to the top of their scope. Functions are fully hoisted, so you can call them before they appear in the file.

var is hoisted with a default value of undefined.

let and const are hoisted too, but kept in a "Temporal Dead Zone" (TDZ) until the engine hits their line of code.

What's the difference between == and ===? == (Loose Equality): Checks value after attempting type coercion. For example, '5' == 5 returns true.

=== (Strict Equality): Checks both value AND type without converting anything. So '5' === 5 returns false.

Can you explain Closures like I'm 5? A closure happens when an inner function remembers variables from its outer (parent) function, even after that parent function has finished executing. function makeCounter() { let count = 0; return function() { count++; return count; }; } const counter = makeCounter(); console.log(counter()); // 1 console.log(counter()); // 2
What is the Event Loop? JavaScript is single-threaded - it can only do one task at a time. The event loop coordinates async operations: Call Stack: Executes synchronous code.

Web APIs: Handles timers, requests, and events in the background.

Callback Queue: Holds callbacks ready to run.

Event Loop: Checks if the Call Stack is empty and moves queued tasks onto it.

Microtasks vs. Macrotasks: What runs first? When asynchronous code completes, it goes into one of two queues: Microtask Queue: Promises (.then(), async/await).

Macrotask Queue: setTimeout, setInterval.

Microtasks always take priority over macrotasks!

What does the this keyword refer to? this refers to the execution context: Global scope: Points to window (or undefined in strict mode).

Object method: Points to the object calling the method.

Arrow Functions: Inherit this lexically from the surrounding code.

What are call, apply, and bind? All three let you explicitly set this: call(): Runs immediately, arguments passed individually.

apply(): Runs immediately, arguments passed as an array.

bind(): Returns a new function with this permanently bound.

What is Prototype / Prototypal Inheritance? In JS, objects inherit properties and methods from other objects through the prototype chain. If a property isn't on the object itself, JS traverses up proto until it finds it or hits null.
What are Promises? A Promise represents a future value. It prevents callback hell and exists in 3 states: Pending, Fulfilled, or Rejected.
How does async/await work? It is syntactic sugar over Promises. async makes a function return a Promise, and await pauses execution until that Promise resolves.
Deep Copy vs. Shallow Copy Shallow Copy: Copies outer properties; nested objects remain linked by reference ({...obj}).

Deep Copy: Recursively copies all levels, creating total independence (structuredClone(obj)).

What is Debouncing and Throttling? Debouncing: Delays execution until user stops action (e.g., typing in search).

Throttling: Limits execution rate (e.g., once every 200ms on scroll).

What are Higher-Order Functions? Functions that either take other functions as parameters (.map(), .filter()) or return a function.
Map vs. Set vs. Object Object: Key-value pairs (string keys).

Map: Key-value pairs allowing any data type as keys.

Set: Collection of unique values (no duplicates).

Event Bubbling vs Capturing Capturing: Event travels from window down to element.

Bubbling: Event travels from element up through parents.

What is Event Delegation? Attaching a single event listener to a parent container to manage events on all existing and future child elements using e.target.
Object.freeze() vs Object.seal() freeze(): Completely immutable (no edits, additions, or deletions).

seal(): Can update existing values, but cannot add or remove properties.

Rest vs Spread Operators (...) Spread: Unpacks values into individual elements ([...arr]).

Rest: Gathers individual values into an array (function(...args)).

What is a Pure Function? A function that always produces the exact same output for the same inputs and causes no side effects outside its scope. Final Thought Interviews are less about memorizing definitions word-for-word and more about showing that you understand how the engine operates under the hood. When you can articulate concepts like closures, event loops, and variable scopes in simple language, interviewers know you truly understand your craft. If you found this guide helpful, consider clapping 👏 and saving it for quick reference before your next tech screen! 🚀

Chrome vs Brave: A Developer's Perspective

Dev Raj Sharma — Fri, 12 Jan 2024 06:59:01 +0000

As developers, choosing the right browser is a crucial decision that impacts our workflow and productivity. Two browsers that often find themselves in the spotlight are Google Chrome and Brave. In this post, let's dive into a comparison between these two, exploring their features and how they cater to the needs of developers.

1. Performance:

Chrome:
Known for its speed, Chrome is a performance powerhouse. It excels in rendering web pages quickly and efficiently.

Brave:
Brave, built on Chromium, inherits some of Chrome's performance benefits. It offers a fast browsing experience, with a focus on blocking ads and trackers to enhance speed.

2. Privacy and Security:

Chrome:
While Chrome has made strides in privacy features, it's associated with Google, which raises concerns for some users. It may collect data for personalized ads and services.

Brave:
Brave puts a strong emphasis on privacy. It blocks ads and trackers by default and offers features like Tor browsing for enhanced anonymity.

3. Customizability:

Chrome:
Chrome has a vast selection of extensions and themes, allowing users to tailor their browsing experience extensively.

Brave:
Brave supports Chrome extensions, making it customizable. However, its primary focus on privacy might limit some extension choices.

4. Built-in Features:

Chrome:
Chrome comes with a variety of built-in tools for developers, including the Developer Tools, which are comprehensive and powerful.

Brave:
Brave inherits the developer tools from Chromium, ensuring compatibility with Chrome extensions. However, it may lack some of the latest features found in Chrome.

5. Rewards and Ad Blocking:

Chrome:
Chrome doesn't have built-in ad-blocking, and users might need extensions for a similar experience.

Brave:
Brave takes a different approach, blocking ads by default and rewarding users with Basic Attention Tokens (BAT) for viewing privacy-respecting ads.

Conclusion:

The choice between Chrome and Brave ultimately depends on individual preferences and priorities. If speed and a wide array of extensions are crucial, Chrome might be the preferred choice. On the other hand, if privacy and ad-blocking are top priorities, Brave stands out.
Both browsers have their merits, and the best choice may vary based on your specific needs as a developer. It's worth trying both to see which aligns better with your workflow and values.>

What's your preferred browser, and why? Share your thoughts in the comments below!

Introducing Project IDX: Revolutionizing Development on the Cloud

Dev Raj Sharma — Wed, 10 Jan 2024 14:26:21 +0000

Developers, brace yourselves for a groundbreaking shift in the development landscape with Project IDX. This experimental, web-based integrated development environment (IDE) is set to transform the way we build and deploy applications. Whether you're a seasoned developer or just starting your coding journey, IDX is here to simplify your development workflow.

What is Project IDX?

Project IDX is not just an IDE; it's a vision for a future where setting up development environments becomes a hassle-free experience. Built on the popular Code OSS project and leveraging the robust infrastructure of Google Cloud, IDX offers fully configurable virtual machines (VMs) to ensure reliability, safety, and complete configurability - all within your browser.

Key Features to Propel Your Development Journey

1. Familiar Environment
IDX provides a familiar environment by being built on the widely used Code OSS project. This familiarity extends to developers who can seamlessly transition into IDX without the steep learning curve.

2. IDX AI - Your Coding Companion
IDX introduces AI into the development process with its AI-powered code suggestions and chat features. Need help generating new code, translating code, or explaining complex snippets? IDX AI has you covered. It even highlights potential license requirements based on the generated code.

3. Effortless Project Creation
Say goodbye to the tedium of starting new projects. IDX supports various frameworks like Angular, Flutter, Next.js, React, Svelte, and Vue, offering templates that make starting your desired app a breeze, all directly from your browser.

4. GitHub Integration
Bring your existing projects into IDX or kickstart your work from public or private GitHub repositories. Seamless integration ensures a smooth transition from your current development setup.

5. Built-In Emulators and Simulators
Developing Flutter apps? IDX comes equipped with Android emulators and iOS simulators right in your workspace. Check your changes and streamline your Flutter development process effortlessly.

6. Direct Deployment
Deploy your web or Flutter web projects directly to Firebase Hosting from your IDX workspace, eliminating the need for additional steps in the deployment pipeline.

7. Collaborative Workspace Sharing (Experimental)
IDX takes collaboration to the next level. Experiment with the experimental workspace sharing feature, inviting others to your workspace with shared access to code, terminals, emulators, and more.

8. Full VM Workspaces
Configure, reproduce, and enjoy ephemeral IDX workspaces that allow you to code from anywhere with a clean, powerful developer setup.

9. Extensions for Enhanced Productivity
IDX comes pre-loaded with extensions to assist you in setting up your workspace. Additionally, explore a variety of extensions available from OpenVSX, enhancing your productivity further.

Unveiling Project IDX: A Game-Changing Coding Playground
Hey fellow devs, brace yourselves for a coding revolution with Project IDX! It's not your ordinary IDE; think of it as your coding sanctuary, making the whole process smoother and more enjoyable. No more grappling with complex setups – IDX has got your back!

Decoding Project IDX:
Imagine Project IDX as a virtual haven for coding, accessible right from your web browser. No fuss, no setup headaches – just pure coding goodness.

The Cool Features:

Familiarity is Key
Ever get that warm and fuzzy feeling using your favorite coding tools? IDX brings you that comfort, built on the foundation of Code OSS. It's like a reliable companion for developers.
Your Coding Sidekick - IDX AI
Say hello to your new coding companion, IDX AI! This intelligent assistant lends a helping hand with code suggestions, translations, and unraveling tricky code. Need a coding buddy? IDX AI has got your back!
Effortless Project Kickoff
Starting a new project doesn't have to be a headache. IDX comes with special templates for various projects – websites, mobile apps, you name it. Just a click, and you're good to go!
GitHub Integration Magic
Already have cool projects on GitHub? IDX works its magic, bringing them into the mix. It's like your GitHub projects seamlessly joining the IDX party.
Play with Emulators
Developing apps for your phone? IDX has built-in play areas for Android and iPhone apps. It's like having virtual phones right on your computer – pretty slick!
Showcase Your Work
Done creating something awesome? With IDX, flaunt your work to others. It's akin to inviting friends to witness your coding prowess, and they can even pitch in if you're up for it!
Streamlined Deployment
Getting your app out there can be tricky, but not with IDX. Send your website or app straight to the internet using Firebase. It's like a shortcut for showcasing your creations!
Collaborative Workspace (Still in the Learning Phase!)
Here's something brand new – invite friends to your coding space! They can see what you're doing, and you can work together. It's like having a coding party online.
Personalize Your Coding Space
Just like decorating your laptop, IDX lets you add cool things to your coding space, making it uniquely yours. Plus, there are extra tools you can add to enhance your coding experience!

Points to Remember:
Before you embark on your IDX journey, heed the cautionary notes. Project IDX is an experimental release, subject to change without notice. It's not intended for production use, but rather an exploration of a new paradigm in app development.
The AI generative code features and Android emulators support come with additional restrictions and disclaimers, emphasizing responsible usage and adherence to specified terms and conditions.

Join the Revolution:

Get Started with Project IDX
Ready to experience the future of development? Join the waitlist and be part of the revolution. Whether you're an AI enthusiast, a seasoned developer, or a curious learner, Project IDX promises to reshape your coding experience.

Optimizing React Application Performance: Best Practices for MERN Stack Developers

Dev Raj Sharma — Tue, 09 Jan 2024 06:08:35 +0000

Introduction

In the fast-paced world of web development, optimizing the performance of your React applications is crucial for delivering a seamless user experience. As MERN (MongoDB, Express.js, React, Node.js) Stack Developers, it's essential to adopt best practices that not only enhance the speed of your applications but also contribute to overall user satisfaction.

1. Code Splitting

What is Code Splitting?
Code splitting is a technique that involves breaking down your JavaScript bundle into smaller, more manageable chunks. By loading only the necessary code for a particular view or feature, you can significantly reduce the initial page load time.

How to Implement Code Splitting in MERN

Use React.lazy and Suspense for dynamic imports of components.
Identify and split large libraries or components that are not immediately needed.
Leverage tools like Webpack for seamless integration.

Real-World Scenarios

Loading specific components only when a user navigates to a certain route.
Optimizing the loading of heavy third-party libraries on demand.

2. Memoization Techniques

Understanding Memoization
Memoization involves caching the results of expensive function calls and returning the cached result when the same inputs occur again. In React, this can prevent unnecessary re-renders and enhance overall application performance.

Using useMemo and useCallback

Use useMemo to memoize the result of expensive computations within functional components.
Apply useCallback to memoize callback functions, preventing unnecessary recreation.

Scenarios for Memoization

Components depending on dynamic data that doesn't change frequently.
Callback functions passed down to child components that remain constant.

3. Lazy Loading

The Significance of Lazy Loading

Lazy loading is the practice of deferring the loading of non-essential resources until they are actually needed. This is particularly impactful in reducing the initial load time of your React application.

Implementation in MERN

Implement dynamic imports for components that are not critical for the initial view.
Consider server-side rendering (SSR) to optimize the first meaningful paint.

Impact on Initial Page Load

Faster loading times, especially for large-scale applications.
Improved perceived performance leading to better user engagement.

4. Efficient Data Fetching

Best Practices for Data Fetching

Minimize unnecessary data fetching by fetching only what is needed for a particular view.
Implement pagination and caching strategies to optimize API calls.
Handle large datasets efficiently, considering factors like virtualization.

Practical Examples

Fetching only essential user data on the dashboard.
Implementing a caching mechanism to store frequently accessed API responses.

5. Bundle Size Optimization

Analyzing and Reducing Bundle Size

Employ tools like tree shaking to eliminate unused code.
Minify and compress JavaScript files to reduce overall bundle size.
Strike a balance between code splitting for performance and its impact on bundle size.

Tips for Developers

Regularly analyze and audit your bundle size.
Prioritize critical code paths for optimization.

Conclusion

In the dynamic landscape of MERN stack development, optimizing React application performance is an ongoing journey. By implementing these best practices, MERN stack developers can not only create faster, more responsive applications but also contribute to a positive user experience. Stay informed about emerging optimization techniques and tools to ensure your applications remain at the forefront of performance standards. Remember, a well-optimized application is a key driver of user satisfaction and retention. Happy coding!

forEach() vs map() in JavaScript

Dev Raj Sharma — Mon, 08 Jan 2024 10:34:25 +0000

Map() function

In JavaScript, the map function is a higher-order function that is used to create a new array by applying a provided function to each element of an existing array. The original array remains unchanged. The map function takes a callback function as its argument, and this callback function is applied to each element of the array.

Here's a basic syntax for the map() function:

let newArray = originalArray.map(callbackFunction);

Square of each elelment of an array

You can also use arrow functions for a more concise syntax:

forEach() method

In JavaScript, the forEach method is used to iterate over elements in an array. It provides a concise way to loop through each element of an array and perform a specified operation for each element.

Here's a basic syntax of the forEach() method:

array.forEach(function(currentValue, index, array){
// Your code here});

Here's an example:

What happen if we try to modify the array using forEach()

The output Will be undefined.

Correct approach of doing it.

When to use which

Your use case will determine whether to use map() or forEach(). The map() provides a new array containing the transformed data, thus you should use it if you intend to modify, alternate, or use the data.But instead of using map(), use forEach() if you won’t require the resulting array.

Basic Array Methods In JavaScript.

Dev Raj Sharma — Sun, 07 Jan 2024 07:53:22 +0000

Lets Create An Array of Integers
let numbers = [5, 1, 7, 3]; console.log(numbers);

[ 5, 1, 7, 3 ]

1. Finding the length of the Array
let lengthOfArray = numbers.length; console.log(lengthOfArray);

2. Sortng the array in ascending order
numbers.sort(); console.log(numbers);

[ 1, 3, 5, 7 ]

3. Adding new element in last of the index
numbers.push(6); console.log(numbers);

[ 1, 3, 5, 7, 6 ]

4. Adding new Element in starting of the array
numbers.unshift(8); console.log(numbers);

[ 8, 1, 3, 5, 7, 6 ]

5. Removing or Deeleting a first element of the array
numbers.shift(); console.log(numbers);

[ 1, 3, 5, 7, 6 ]

6. Removing or Deleting a last element of the array
numbers.pop(); console.log(numbers);
[ 1, 3, 5, 7 ]

7. Finding element of the targeted index

let index = 2; console.log(At index of ${index} element is ${numbers.at(index)});

At index of 2 element is 5

8. Merging two or more array
const array1 = [1,2,3,4,5]; const array2 = [6,7,8,9]; const newArray = array1.concat(array2); console.log(newArray)

[1, 2, 3, 4, 5 ,6, 7, 8, 9]