javascript basics interview questions Part 1: Mastering the Basics Covering all essential topics from basics to advanced, including ES6, closures, hoisting, and more. Perfect for frontend developers and coding interviews.
🔥 Introduction
javascript basics interview questions Whether you’re preparing for your next frontend developer interview or just brushing up on your skills, mastering JavaScript interview questions is crucial. In this guide, we’ll cover basic to advanced JavaScript topics, including syntax, ES6 features, asynchronous programming, OOP, functional programming, DOM, event handling, and more.
🧠 javascript basics interview questions
Table of Contents
1. What is JavaScript?
Answer:
JavaScript is a high-level, interpreted programming language used to create dynamic and interactive web pages. It is a core technology of the web along with HTML and CSS.
2. What are the data types in JavaScript?
Answer:
JavaScript supports:
- Primitive Types: String, Number, BigInt, Boolean, Undefined, Symbol, Null
- Non-Primitive (Reference) Types: Objects, Arrays, Functions
3. What is the difference between var, let, and const?
Answer:
| Keyword | Scope | Hoisting | Reassignment | Redeclaration |
|---|---|---|---|---|
var | Function | Yes | Yes | Yes |
let | Block | No | Yes | No |
const | Block | No | No | No |
4. Explain hoisting in JavaScript.
Answer:
Hoisting is JavaScript’s default behavior of moving declarations to the top of the current scope. Only declarations are hoisted, not initializations.
console.log(x); // undefined
var x = 10;
5. What is the difference between == and ===?
Answer:
==compares values after type coercion===compares both value and type
'5' == 5 // true
'5' === 5 // false
⚙️ JavaScript ES6 Interview Questions
6. What are template literals in JavaScript?
Answer:
Template literals are enclosed by backticks (`) and allow interpolation using ${}.
const name = "John";
console.log(`Hello, ${name}!`);
7. Explain arrow functions in ES6.
Answer:
Arrow functions are a concise way to write functions and they do not bind their own this.
const add = (a, b) => a + b;
8. What is destructuring in JavaScript?
Answer:
Destructuring allows unpacking values from arrays or properties from objects into distinct variables.
const [a, b] = [1, 2];
const {name, age} = {name: 'John', age: 30};
9. What are default parameters?
Answer:
Function parameters can have default values if no argument is provided.
function greet(name = "Guest") {
console.log(`Hello, ${name}`);
}
10. Explain the spread and rest operators.
Answer:
- Spread (
...): Expands arrays/objects. - Rest (
...): Collects arguments into an array.
// Spread
const arr1 = [1, 2];
const arr2 = [...arr1, 3];
// Rest
function sum(...numbers) {
return numbers.reduce((a, b) => a + b);
}
🔄 Asynchronous JavaScript Interview Questions
11. What is the difference between synchronous and asynchronous code?
Answer:
- Synchronous: Executes line by line.
- Asynchronous: Non-blocking operations using callbacks, promises, or async/await.
12. What are Promises in JavaScript?
Answer:
A Promise is an object representing the eventual completion or failure of an asynchronous operation.
const promise = new Promise((resolve, reject) => {
setTimeout(() => resolve("Done"), 1000);
});
13. What is async/await in JavaScript?
Answer:async functions return a promise and await pauses the execution until the promise is resolved.
async function fetchData() {
const response = await fetch('/api/data');
const data = await response.json();
}
14. What is the event loop in JavaScript?
Answer:
The event loop handles asynchronous callbacks by moving tasks from the event queue to the call stack when it’s empty.
15. What is a callback function?
Answer:
A function passed as an argument to another function and executed later.
function greet(name, callback) {
callback(`Hello, ${name}`);
}
📦 More Parts Coming…
This is just Part 1. Upcoming parts will cover:
- Advanced JavaScript (Closures, Scope, IIFE, Currying, Memoization)
- OOP in JavaScript
- DOM Manipulation & Events
- Error Handling & Debugging
- JavaScript Design Patterns
- Coding Challenges
- And much more…
javascript basics interview questions Part 1: Mastering the Basics
Part 2, which will cover advanced JavaScript topics like closures, scope, prototype, etc.?
