🔰 Basic ES6 Interview Questions

1. What is ES6?

👉 ES6 (ECMAScript 2015) is the 6th version of JavaScript with modern features like let, const, arrow functions, etc.

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2. Difference between var, let, and const?

Feature	var	let	const
Scope	Function	Block	Block
Reassign	✅	✅	❌
Hoisting	Yes	Yes (TDZ)	Yes (TDZ)

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3. What is Temporal Dead Zone (TDZ)?

👉 Time between variable declaration and initialization where access causes error.

console.log(a); // ❌ error
let a = 10;

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4. What are arrow functions?

👉 Short syntax for functions and no this binding.

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5. Difference between normal function and arrow function?

👉 Arrow functions:

• No this
• No arguments
• Cannot be used as constructor

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🔥 Intermediate Questions

6. What is destructuring?

👉 Extract values from arrays/objects.

let {name} = {name: "Aditya"};

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7. What is spread operator?

👉 Expands values.

let arr = [...[1,2,3]];

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8. What is rest operator?

👉 Collects values.

function sum(...nums) {}

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9. Difference between spread and rest?

👉 Spread = expand
👉 Rest = collect

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10. What are template literals?

👉 Backticks (`) used for dynamic strings.

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11. What are default parameters?

function greet(name = "Guest") {}

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12. What are modules in ES6?

👉 Split code using import and export

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🚀 Advanced ES6 Questions

13. What is this behavior in arrow functions?

👉 Arrow functions inherit this from parent scope.

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14. Can we use arrow function as constructor?

👉 ❌ No

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15. What is Symbol in ES6?

👉 Unique and immutable data type.

let id = Symbol("id");

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16. What are iterators?

👉 Objects that allow looping (next() method).

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17. What are generators?

👉 Functions that pause using yield.

function* gen() {
  yield 1;
}

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18. What is Map in ES6?

👉 Key-value collection (any type key allowed)

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19. What is Set?

👉 Collection of unique values

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20. Difference between Map and Object?

Map	Object
Any key type	String keys
Ordered	Not guaranteed
Better performance	Less efficient

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💡 Coding-Based Questions

21. Swap variables using ES6

let a = 1, b = 2;
[a, b] = [b, a];

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22. Merge arrays

let arr = [...arr1, ...arr2];

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23. Clone object

let newObj = {...oldObj};

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🎯 Pro Tip for Interview

👉 Most asked topics:

• let vs const vs var
• Arrow functions & this
• Destructuring
• Spread vs Rest
• Modules