Top JavaScript Interview Questions & Answers

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115 pages · 289 questions

What Is JavaScript and Where Does It Run?
3 questions 1 easy 1 med 1 hardFree
JavaScript vs Java: Any Relation?
2 questions 1 easy 1 medFree
How Does the JavaScript Engine Run Code?
3 questions 1 easy 1 med 1 hardFree
What Changed with ES6 and Later?
2 questions 1 easy 1 medFree
Browser, Node and Beyond
3 questions 1 easy 1 med 1 hardFree
var vs let vs const
2 questions 1 easy 1 medFree
What Are JavaScript's Data Types?
3 questions 1 easy 1 med 1 hardFree
Why Does typeof null Return "object"?
2 questions 1 easy 1 medFree
What Does Strict Mode Change?
3 questions 1 easy 1 med 1 hardFree
Are Semicolons Required in JavaScript?
2 questions 1 easy 1 medFree
How Does Type Coercion Work?
3 questions 1 easy 1 med 1 hardFree
== vs === in JavaScript
2 questions 1 easy 1 medFree
Explicit vs Implicit Conversion
3 questions 1 easy 1 med 1 hardFree
Why Is NaN Not Equal to Itself?
2 questions 1 easy 1 medFree
What Gets Hoisted in JavaScript?
3 questions 1 easy 1 med 1 hardFree
What Is the Temporal Dead Zone?
2 questions 1 easy 1 medFree
Spread vs Rest Syntax
3 questions 1 easy 1 med 1 hardFree
How Does Destructuring Work?
2 questions 1 easy 1 medFree
What Can Template Literals Do?
3 questions 1 easy 1 med 1 hardFree
When Do You Need Symbol and BigInt?
2 questions 1 easy 1 medFree
How Do Functions Work in JavaScript?
3 questions 1 easy 1 med 1 hardFree
Function Declaration vs Expression
2 questions 1 easy 1 medFree
Arrow Functions vs Regular Functions
3 questions 1 easy 1 med 1 hardFree
What Is an IIFE and Why Use One?
2 questions 1 easy 1 medFree
How Do Callbacks Pass Behavior?
3 questions 1 easy 1 med 1 hardFree
What Makes a Function Higher-Order?
2 questions 1 med 1 hardFree
How Do Default Parameters Evaluate?
3 questions 1 easy 1 med 1 hardFree
What Is the arguments Object?
2 questions 1 easy 1 medFree
How Does Recursion Work in JavaScript?
3 questions 1 easy 1 med 1 hardFree
What Is a Pure Function?
2 questions 1 med 1 hardFree
How Do Arrays Behave in JavaScript?
3 questions 1 easy 1 med 1 hardFree
map vs filter vs reduce
2 questions 1 easy 1 medFree
Which Iteration Method Fits Which Job?
3 questions 1 easy 1 med 1 hardFree
find() vs filter()
2 questions 1 med 1 hardFree
slice() vs splice()
3 questions 1 easy 1 med 1 hardFree
How Do You Flatten Nested Arrays?
2 questions 1 easy 1 medFree
How Do You Remove Duplicates from an Array?
3 questions 1 easy 1 med 1 hardFree
How Does sort() Actually Sort?
2 questions 1 med 1 hardFree
Array.from() and Array.of()
3 questions 1 easy 1 med 1 hardFree
Destructuring Arrays in Practice
2 questions 1 easy 1 medFree
How Do Objects Work in JavaScript?
3 questions 1 easy 1 med 1 hardFree
Dot vs Bracket Notation
2 questions 1 med 1 hardFree
Shallow vs Deep Copy of Objects
3 questions 1 easy 1 med 1 hardFree
What Does Object.freeze Guarantee?
2 questions 1 easy 1 medFree
How Does ?. Prevent Crashes?
3 questions 1 easy 1 med 1 hardFree
?? vs || in JavaScript
2 questions 1 med 1 hardFree
keys(), values() and entries()
3 questions 1 easy 1 med 1 hardFree
How Do References Differ from Values?
2 questions 1 easy 1 medFree
How Do Methods Bind this?
3 questions 1 easy 1 med 1 hardFree
stringify() and parse() in Practice
2 questions 1 med 1 hardFree
How Do Strings Behave in JavaScript?
3 questions 1 easy 1 med 1 hardFree
Which String Methods Come Up Most?
2 questions 1 easy 1 medFree
Why Are Strings Immutable?
3 questions 1 easy 1 med 1 hardFree
How Do You Reverse a String?
2 questions 1 med 1 hardFree
Checking Substrings Cleanly
3 questions 1 easy 1 med 1 hardFree
toFixed, toPrecision and Parsing
2 questions 1 easy 1 medFree
The Math Object in Practice
3 questions 1 easy 1 med 1 hardFree
How Do Dates Behave in JavaScript?
2 questions 1 med 1 hardFree
Regex Questions That Actually Get Asked
3 questions 1 easy 1 med 1 hardFree
import/export Syntax Essentials
2 questions 1 easy 1 medFree
What Is the DOM?
3 questions 1 easy 1 med 1 hardFree
querySelector vs getElementById
2 questions 1 med 1 hardFree
How Do You Change the Page with JS?
3 questions 1 easy 1 med 1 hardFree
Building Nodes from Scratch
2 questions 1 easy 1 medFree
How Do Event Listeners Work?
3 questions 1 easy 1 med 1 hardFree
Why Delegate Events?
2 questions 1 med 1 hardFree
Bubbling vs Capturing Explained
3 questions 1 easy 1 med 1 hardFree
preventDefault vs stopPropagation
2 questions 1 easy 1 medFree
data-* Attributes and dataset
3 questions 1 easy 1 med 1 hardFree
What Causes Reflows?
2 questions 1 med 1 hardFree
What Does Asynchronous Mean in JS?
3 questions 1 easy 1 med 1 hardFree
From Callbacks to Promises
2 questions 1 easy 1 medFree
What States Can a Promise Have?
3 questions 1 easy 1 med 1 hardFree
How Does async/await Work?
2 questions 1 med 1 hardFree
all vs race vs allSettled
3 questions 1 easy 1 med 1 hardFree
How Does fetch Work?
2 questions 1 easy 1 medFree
What Is the Event Loop?
3 questions 1 easy 1 med 1 hardFree
Microtasks vs Macrotasks
2 questions 1 med 1 hardFree
Escaping Callback Hell
3 questions 1 easy 1 med 1 hardFree
Catching Errors in Async Code
2 questions 1 easy 1 medFree
What Is a Closure?
3 questions 1 easy 1 med 1 hardFree
Where Do Closures Earn Their Keep?
2 questions 1 med 1 hardFree
How Is this Decided?
3 questions 1 easy 1 med 1 hardFree
call vs apply vs bind
2 questions 1 easy 1 medFree
What Is the Prototype Chain?
3 questions 1 easy 1 med 1 hardFree
How Does Prototypal Inheritance Work?
2 questions 1 med 1 hardFree
How Do Classes Relate to Prototypes?
3 questions 1 easy 1 med 1 hardFree
How Do extends and super Work?
2 questions 1 easy 1 medFree
What Does new Actually Do?
3 questions 1 easy 1 med 1 hardFree
TypeError, ReferenceError and Friends
3 questions 1 easy 1 med 1 hardFree
How Do try/catch/finally Interact?
2 questions 1 med 1 hardFree
What Can You Throw in JavaScript?
3 questions 1 easy 1 med 1 hardFree
Building Custom Error Classes
2 questions 1 easy 1 medFree
Catching Unhandled Rejections
3 questions 1 easy 1 med 1 hardFree
How Do You Debug in DevTools?
2 questions 1 med 1 hardFree
Beyond console.log
3 questions 1 easy 1 med 1 hardFree
Patterns That Prevent Bugs
2 questions 1 easy 1 medFree
Handling Errors Across async Flows
3 questions 1 easy 1 med 1 hardFree
ESM vs CommonJS
3 questions 1 easy 1 med 1 hardFree
Named, Default and Re-exports
3 questions 1 easy 1 med 1 hardFree
localStorage vs sessionStorage
2 questions 1 med 1 hardFree
How Do Cookies Work from JS?
3 questions 1 easy 1 med 1 hardFree
Which Web APIs Matter Most?
2 questions 1 easy 1 medFree
Timers and Their Gotchas
3 questions 1 easy 1 med 1 hardFree
Debounce vs Throttle
2 questions 1 med 1 hardFree
Parsing URLs with the URL API
3 questions 1 easy 1 med 1 hardFree
fetch vs axios: What Differs?
2 questions 1 easy 1 medFree
How Do You Prepare for a JS Interview?
3 questions 1 easy 1 med 1 hardFree
Predict-the-Output Questions
2 questions 1 med 1 hardFree
Implementing Debounce from Scratch
3 questions 1 easy 1 med 1 hardFree
Array Drills from Real Interviews
2 questions 1 easy 1 medFree
Building a Tiny Promise
3 questions 1 easy 1 med 1 hardFree
Discussing JS Projects Confidently
2 questions 1 med 1 hardFree
Newest Features Worth Knowing
3 questions 1 easy 1 med 1 hardFree
A DOM Exercise They Love to Ask
2 questions 2 medFree

What Is JavaScript and Where Does It Run?

JavaScript vs Java: Any Relation?

How Does the JavaScript Engine Run Code?

What Changed with ES6 and Later?

Browser, Node and Beyond

var vs let vs const

What Are JavaScript's Data Types?

Why Does typeof null Return "object"?

What Does Strict Mode Change?

Are Semicolons Required in JavaScript?

How Does Type Coercion Work?

== vs === in JavaScript

Explicit vs Implicit Conversion

Why Is NaN Not Equal to Itself?

What Gets Hoisted in JavaScript?

What Is the Temporal Dead Zone?

Spread vs Rest Syntax

How Does Destructuring Work?

What Can Template Literals Do?

When Do You Need Symbol and BigInt?

How Do Functions Work in JavaScript?

Function Declaration vs Expression

Arrow Functions vs Regular Functions

What Is an IIFE and Why Use One?

How Do Callbacks Pass Behavior?

What Makes a Function Higher-Order?

How Do Default Parameters Evaluate?

What Is the arguments Object?

How Does Recursion Work in JavaScript?

What Is a Pure Function?

How Do Arrays Behave in JavaScript?

map vs filter vs reduce

Which Iteration Method Fits Which Job?

find() vs filter()

slice() vs splice()

How Do You Flatten Nested Arrays?

How Do You Remove Duplicates from an Array?

How Does sort() Actually Sort?

Array.from() and Array.of()

Destructuring Arrays in Practice

How Do Objects Work in JavaScript?

Dot vs Bracket Notation

Shallow vs Deep Copy of Objects

What Does Object.freeze Guarantee?

How Does ?. Prevent Crashes?

?? vs || in JavaScript

keys(), values() and entries()

How Do References Differ from Values?

How Do Methods Bind this?

stringify() and parse() in Practice

How Do Strings Behave in JavaScript?

Which String Methods Come Up Most?

Why Are Strings Immutable?

How Do You Reverse a String?

Checking Substrings Cleanly

toFixed, toPrecision and Parsing

The Math Object in Practice

How Do Dates Behave in JavaScript?

Regex Questions That Actually Get Asked

import/export Syntax Essentials

What Is the DOM?

querySelector vs getElementById

How Do You Change the Page with JS?

Building Nodes from Scratch

How Do Event Listeners Work?

Why Delegate Events?

Bubbling vs Capturing Explained

preventDefault vs stopPropagation

data-* Attributes and dataset

What Causes Reflows?

What Does Asynchronous Mean in JS?

From Callbacks to Promises

What States Can a Promise Have?

How Does async/await Work?

all vs race vs allSettled

How Does fetch Work?

What Is the Event Loop?

Microtasks vs Macrotasks

Escaping Callback Hell

Catching Errors in Async Code