🔰 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.
2. Difference between var, let, and const?
| Feature | var | let | const |
|---|---|---|---|
| Scope | Function | Block | Block |
| Reassign | ✅ | ✅ | ❌ |
| Hoisting | Yes | Yes (TDZ) | Yes (TDZ) |
3. What is Temporal Dead Zone (TDZ)?
👉 Time between variable declaration and initialization where access causes error.
console.log(a); // ❌ error
let a = 10;4. What are arrow functions?
👉 Short syntax for functions and no this binding.
5. Difference between normal function and arrow function?
👉 Arrow functions:
- No
this - No
arguments - Cannot be used as constructor
🔥 Intermediate Questions
6. What is destructuring?
👉 Extract values from arrays/objects.
let {name} = {name: "Aditya"};7. What is spread operator?
👉 Expands values.
let arr = [...[1,2,3]];8. What is rest operator?
👉 Collects values.
function sum(...nums) {}9. Difference between spread and rest?
👉 Spread = expand
👉 Rest = collect
10. What are template literals?
👉 Backticks (`) used for dynamic strings.
11. What are default parameters?
function greet(name = "Guest") {}12. What are modules in ES6?
👉 Split code using import and export
🚀 Advanced ES6 Questions
13. What is this behavior in arrow functions?
👉 Arrow functions inherit this from parent scope.
14. Can we use arrow function as constructor?
👉 ❌ No
15. What is Symbol in ES6?
👉 Unique and immutable data type.
let id = Symbol("id");16. What are iterators?
👉 Objects that allow looping (next() method).
17. What are generators?
👉 Functions that pause using yield.
function* gen() {
yield 1;
}18. What is Map in ES6?
👉 Key-value collection (any type key allowed)
19. What is Set?
👉 Collection of unique values
20. Difference between Map and Object?
| Map | Object |
|---|---|
| Any key type | String keys |
| Ordered | Not guaranteed |
| Better performance | Less efficient |
💡 Coding-Based Questions
21. Swap variables using ES6
let a = 1, b = 2;
[a, b] = [b, a];22. Merge arrays
let arr = [...arr1, ...arr2];23. Clone object
let newObj = {...oldObj};🎯 Pro Tip for Interview
👉 Most asked topics:
- let vs const vs var
- Arrow functions &
this - Destructuring
- Spread vs Rest
- Modules
