1️⃣ What is Scope in JavaScript?

Answer:
Scope determines where variables are accessible.

Global Scope → accessible everywhere
Function Scope → inside function
Block Scope → inside {} (let, const)

let a = 10;function test() {
  let b = 20;
}

👉 b is not accessible outside the function.

2️⃣ What is Hoisting?

Answer:
Hoisting is JavaScript’s default behavior of moving declarations to the top.

console.log(a); // undefined
var a = 5;

👉 var is hoisted with undefined

⚠️ let and const are hoisted but in Temporal Dead Zone

3️⃣ What is a Closure?

Answer:
A closure is a function that remembers variables from its outer scope.

function outer() {
  let count = 0;  return function () {
    count++;
    return count;
  };
}let fn = outer();
fn(); // 1
fn(); // 2

👉 Used in:

Data hiding
Private variables
Callbacks

4️⃣ What is Execution Context?

Answer:
Execution context is the environment where JavaScript code runs.

Types:

Global Execution Context
Function Execution Context

Phases:

Memory creation
Code execution

5️⃣ What is Call Stack?

Answer:
Call stack is a structure that keeps track of function calls (LIFO).

function a() { b(); }
function b() { console.log("Hi"); }a();

👉 Stack:
a → b → console.log

6️⃣ What is `this` keyword?

Answer:
this refers to the object that calls the function.

let obj = {
  name: "Aditya",
  show() {
    console.log(this.name);
  }
};

Important cases:

Object → refers to object
Function → window / undefined
Arrow → inherits from parent

7️⃣ Difference between `call`, `apply`, and `bind`?

Answer:

function greet(city) {
  console.log(this.name + " from " + city);
}let user = { name: "Aditya" };greet.call(user, "Delhi");
greet.apply(user, ["Delhi"]);let fn = greet.bind(user);
fn("Delhi");

👉 Difference:

call → arguments separately
apply → arguments as array
bind → returns new function

8️⃣ What is Prototype?

Answer:
Prototype is an object from which other objects inherit properties.

function Person(name) {
  this.name = name;
}Person.prototype.sayHi = function () {
  console.log("Hi " + this.name);
};

9️⃣ What is Prototypal Inheritance?

Answer:
Objects inherit properties from another object.

let parent = {
  greet() {
    console.log("Hello");
  }
};let child = Object.create(parent);
child.greet();

🔟 What is the difference between `==` and `===`?

Answer:

== → compares value (type conversion happens)
=== → compares value + type

"5" == 5   // true
"5" === 5  // false

1️⃣1️⃣ What is Event Loop? (Bonus 🔥)

Answer:
Event loop handles async operations in JavaScript.

👉 Flow:

Call Stack
Web APIs
Callback Queue
Event Loop

1️⃣2️⃣ What is Temporal Dead Zone?

Answer:
Time between variable hoisting and initialization.

console.log(a); // Error
let a = 10;

1️⃣3️⃣ What are Arrow Functions?

Answer:
Short syntax functions that don’t have their own this.

const add = (a, b) => a + b;

1️⃣4️⃣ What is Difference: var vs let vs const?

Feature	var	let	const
Scope	Function	Block	Block
Hoisting	Yes	Yes (TDZ)	Yes (TDZ)
Reassign	Yes	Yes	No

1️⃣5️⃣ What is a Higher Order Function?

Answer:
Function that takes another function as argument or returns a function.

function greet(fn) {
  fn();
}

🚀 Pro Tip for Interviews

Focus on:

Writing code
Explaining output
Real-world examples

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Advanced JavaScript Interview Q&A