Question 1

What is the difference between `==` and `===` in JavaScript?

Accepted Answer

`==` checks for value equality with type coercion, while `===` checks for both value and type equality without coercion.

Question 2

What are arrow functions and how do they differ from regular functions?

Accepted Answer

Arrow functions are a shorthand for writing functions. They do not bind their own `this`, `arguments`, or `super`, and cannot be used as constructors.

Question 3

What is the difference between `setTimeout` and `setInterval`?

Accepted Answer

`setTimeout` runs a function once after a delay. `setInterval` runs it repeatedly at specified intervals until stopped with `clearInterval()`.

Question 4

How do you reverse a string in JavaScript?

Accepted Answer

Use `.split('')`, `.reverse()`, and `.join('')` to reverse the characters of the string.

Question 5

How do you add a click event to a button using JavaScript?

Accepted Answer

Use `addEventListener` to attach a function to the button's click event.

Question 6

What is hoisting in JavaScript?

Accepted Answer

Hoisting is JavaScript's behavior of moving declarations to the top of their scope during compilation. Variables declared with `var` are hoisted but initialized as `undefined`; `let` and `const` are hoisted but not initialized, causing a temporal dead zone.

Question 7

Explain closures in JavaScript with an example.

Accepted Answer

A closure is the combination of a function bundled with references to its surrounding state (lexical environment). It allows inner functions to access outer function's variables even after the outer function has returned.

Question 8

What is the difference between `null` and `undefined`?

Accepted Answer

`undefined` means a variable has been declared but not assigned a value. `null` is an assignment value representing no value. `typeof null` returns 'object' (a historical bug).

Question 9

What are Promises and how do they work?

Accepted Answer

A Promise represents a value that may be available now, later, or never. It has three states: pending, fulfilled, rejected. Methods: `then()`, `catch()`, `finally()`.

Question 10

What are template literals and how are they used?

Accepted Answer

Template literals use backticks (``) and allow embedded expressions (`${}`). They support multi-line strings and string interpolation.

JavaScript Coding Interview Questions & Answers

What is the difference between `==` and `===` in JavaScript?

What are arrow functions and how do they differ from regular functions?

What is the difference between `setTimeout` and `setInterval`?

How do you reverse a string in JavaScript?

How do you add a click event to a button using JavaScript?

What is hoisting in JavaScript?

Explain closures in JavaScript with an example.

What is the difference between `null` and `undefined`?

What are Promises and how do they work?

What are template literals and how are they used?

What is the Event Loop in JavaScript?

Explain `async/await` and how it differs from Promises.

What is event delegation and why is it useful?

How do you deep copy an object in JavaScript?

Write a function to flatten a nested array.

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