🚀 50 JavaScript Interview Q&A

Master JavaScript with these must-know questions!

🔹 Basics

1️⃣ `var`, `let`, `const` – Scope & reassignability

2️⃣ Hoisting – Moves declarations to the top

3️⃣ Closures – Functions remembering outer scope

4️⃣ `==` vs `===` – Loose vs strict equality

5️⃣ `this` – Context-based reference

🔹 Functions & Objects

6️⃣ Arrow functions – No own `this`

7️⃣ `.map()` vs `.forEach()` – Returns vs iterates

8️⃣ Spread (`…`) – Expands elements

9️⃣ Destructuring – Extract values easily

🔟 Event delegation – Handling child events at parent

🔹 Async & Promises

1️⃣1️⃣ Promise states – Pending, Fulfilled, Rejected

1️⃣2️⃣ `async/await` – Synchronous-looking async code

1️⃣3️⃣ `setTimeout` vs `setInterval` – Delay vs repeat

1️⃣4️⃣ Error handling – `try…catch` in async functions

1️⃣5️⃣ `fetch()` – API calls with promises

🔹 DOM & Events

1️⃣6️⃣ Querying elements – `document.querySelector()`

1️⃣7️⃣ Event bubbling & capturing – Propagation flow

1️⃣8️⃣ `event.preventDefault()` – Stops default action

1️⃣9️⃣ `event.stopPropagation()` – Stops bubbling

2️⃣0️⃣ Virtual DOM – Efficient UI updates

🔹 Advanced Topics

2️⃣1️⃣ Higher-order functions – Functions taking/returning functions

2️⃣2️⃣ Functional programming – Treats functions as first-class citizens

2️⃣3️⃣ Memory leaks – Unused objects consuming memory

2️⃣4️⃣ Call stack – Function execution tracking

2️⃣5️⃣ Event loop – Handles async tasks

💡 Tip: Practice coding on LeetCode & CodeSandbox!

What Undercode Say

JavaScript is a cornerstone of modern web development, and mastering it is essential for any developer. Understanding core concepts like hoisting, closures, and the event loop can significantly improve your coding efficiency. For instance, knowing the difference between `==` and `===` can prevent subtle bugs in your code. Similarly, mastering asynchronous programming with `async/await` and Promises is crucial for handling API calls and other time-consuming tasks.

To practice, use commands like `node .js` to run JavaScript files in your terminal. For debugging, tools like `console.log()` and `debugger` are invaluable. Additionally, exploring the DOM with `document.querySelector()` and manipulating it with methods like `.addEventListener()` can enhance your front-end skills.

For advanced users, diving into functional programming concepts like higher-order functions and memory management can optimize performance. Tools like `Chrome DevTools` can help identify memory leaks using the `Memory` tab.

Finally, always test your code in different environments. Use `npm init -y` to set up a Node.js project and `npm install ` to add dependencies. For API testing, tools like `Postman` or `curl` commands can be handy.

Keep practicing, and don’t forget to explore resources like MDN Web Docs for in-depth knowledge. Happy coding!

References:

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