Are you preparing for a JavaScript interview in 2025? Whether you’re a newbie or a seasoned developer, interviews can feel tricky\u2014especially when JavaScript is involved. But don’t worry, we\u2019ve got you covered!<\/p>\n\n\n\n
In this blog, we\u2019ve compiled the top 100 JavaScript interview questions you will most likely face this year. From the basics to advanced topics and even popular frameworks like React and Angular, this guide will help you feel confident and ready to tackle any question. Let’s get started.<\/p>\n\n\n\n
This section is perfect if you\u2019re starting your JavaScript<\/a> journey or brushing up on the basics! These questions cover the fundamental concepts of JavaScript that form the foundation of the language. Nail these, and you\u2019ll have a strong starting point for your interview. Let\u2019s get started!<\/p>\n\n\n\n Answer: Key Points:<\/strong><\/p>\n\n\n\n Answer: Key Points:<\/strong><\/p>\n\n\n\n Answer: Key Points:<\/strong><\/p>\n\n\n\n Answer: Key Points:<\/strong><\/p>\n\n\n\n Answer:<\/strong><\/p>\n\n\n\n Example: Answer: Key Points:<\/strong><\/p>\n\n\n\n Answer:<\/strong><\/p>\n\n\n\n Answer: Example:<\/strong><\/p>\n\n\n\n typeof 42; \/\/ “number”<\/p>\n\n\n\n typeof “hello”; \/\/ “string”<\/p>\n\n\n\n typeof undefined; \/\/ “undefined”<\/p>\n\n\n\n Answer: Key Points:<\/strong><\/p>\n\n\n\n Answer: Key Points:<\/strong><\/p>\n\n\n\n Example:<\/strong><\/p>\n\n\n\n let fruits = [“apple”, “banana”, “cherry”];<\/p>\n\n\n\n Answer: Key Points:<\/strong><\/p>\n\n\n\n Answer:<\/strong><\/p>\n\n\n\n Answer: Example:<\/strong><\/p>\n\n\n\n button.addEventListener(“click”, function() {<\/p>\n\n\n\n alert(“Button clicked!”);<\/p>\n\n\n\n });<\/p>\n\n\n\n Answer: Example:<\/strong><\/p>\n\n\n\n function greet(name, callback) {<\/p>\n\n\n\n console.log(“Hello, ” + name);<\/p>\n\n\n\n callback();<\/p>\n\n\n\n }<\/p>\n\n\n\n Answer: Answer: Answer: Example:<\/strong><\/p>\n\n\n\n let name = “John”;<\/p>\n\n\n\n Answer: Answer: Example:<\/strong><\/p>\n\n\n\n let name = “John”;<\/p>\n\n\n\n console.log(`Hello, ${name}!`);<\/p>\n\n\n\n Answer:<\/strong><\/p>\n\n\n\n In this section, we\u2019ll dive into intermediate-level JavaScript concepts. These questions go beyond the basics and focus on real-world scenarios you might face as a developer. Understanding these topics will not only help you during interviews but also give you a deeper grasp of JavaScript\u2019s power and flexibility. Let\u2019s get started!<\/p>\n\n\n\n Answer:<\/strong><\/p>\n\n\n\n Example:<\/strong><\/p>\n\n\n\n ‘5’ == 5; \/\/ true (because ‘5’ is converted to a number)<\/p>\n\n\n\n ‘5’ === 5; \/\/ false (different types)<\/p>\n\n\n\n Answer: Use Case: Example:<\/strong><\/p>\n\n\n\n function outer() {<\/p>\n\n\n\n let counter = 0;<\/p>\n\n\n\n return function inner() {<\/p>\n\n\n\n counter++;<\/p>\n\n\n\n console.log(counter);<\/p>\n\n\n\n };<\/p>\n\n\n\n }<\/p>\n\n\n\n const increment = outer();<\/p>\n\n\n\n increment(); \/\/ 1<\/p>\n\n\n\n increment(); \/\/ 2<\/p>\n\n\n\n Answer: Use Case: Example:<\/strong><\/p>\n\n\n\n document.querySelector(‘button’).addEventListener(‘click’, function(event) {<\/p>\n\n\n\n alert(‘Button clicked!’);<\/p>\n\n\n\n });<\/p>\n\n\n\n Answer: Use Case: Example:<\/strong><\/p>\n\n\n\n document.querySelector(‘#parent’).addEventListener(‘click’, function(event) {<\/p>\n\n\n\n if (event.target && event.target.matches(‘button.classname’)) {<\/p>\n\n\n\n console.log(‘Button clicked!’);<\/p>\n\n\n\n }<\/p>\n\n\n\n });<\/p>\n\n\n\n Answer: Use Case: Example:<\/strong><\/p>\n\n\n\n let promise = new Promise(function(resolve, reject) {<\/p>\n\n\n\n let success = true;<\/p>\n\n\n\n if(success) {<\/p>\n\n\n\n resolve(“Data loaded”);<\/p>\n\n\n\n } else {<\/p>\n\n\n\n reject(“Error”);<\/p>\n\n\n\n }<\/p>\n\n\n\n });<\/p>\n\n\n\n promise.then(function(result) {<\/p>\n\n\n\n console.log(result); \/\/ Data loaded<\/p>\n\n\n\n }).catch(function(error) {<\/p>\n\n\n\n console.log(error); \/\/ Error<\/p>\n\n\n\n });<\/p>\n\n\n\n Answer:<\/strong><\/p>\n\n\n\n Example:<\/strong><\/p>\n\n\n\n let a;<\/p>\n\n\n\n console.log(a); \/\/ undefined<\/p>\n\n\n\n let b = null;<\/p>\n\n\n\n console.log(b); \/\/ null<\/p>\n\n\n\n
\n\n\n\n<\/a>1. What is JavaScript?<\/strong><\/h4>\n\n\n\n
<\/strong>JavaScript is a programming language used to make web pages interactive. It allows you to add features like buttons, animations, and dynamic content to websites.<\/p>\n\n\n\n\n
\n\n\n\n<\/a>2. What are variables in JavaScript?<\/strong><\/h4>\n\n\n\n
<\/strong>Variables are containers used to store data that can be used later in your program.<\/p>\n\n\n\n\n
\n\n\n\n<\/a>3. Explain <\/strong>let<\/strong>, <\/strong>var<\/strong>, and <\/strong>const<\/strong>.<\/strong><\/h4>\n\n\n\n
<\/strong>These are keywords used to declare variables, but they behave differently.<\/p>\n\n\n\n\n
\n\n\n\n<\/a>4. What is <\/strong>NaN<\/strong> in JavaScript?<\/strong><\/h4>\n\n\n\n
<\/strong>NaN stands for “Not a Number” and appears when you try to do a mathematical operation with a non-numeric value.<\/p>\n\n\n\n\n
\n\n\n\n<\/a>5. What is the difference between <\/strong>==<\/strong> and <\/strong>===<\/strong>?<\/strong><\/h4>\n\n\n\n
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<\/strong>5 == ‘5’ \u2192 true (values match, types ignored).
5 === ‘5’ \u2192 false (values match, but types differ).<\/p>\n\n\n\n
\n\n\n\n<\/a>6. What are data types in JavaScript?<\/strong><\/h4>\n\n\n\n
<\/strong>JavaScript has different data types to store different kinds of values.<\/p>\n\n\n\n\n
\n\n\n\n<\/a>7. What is the difference between <\/strong>null<\/strong> and <\/strong>undefined<\/strong>?<\/strong><\/h4>\n\n\n\n
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\n\n\n\n<\/a>8. What is the <\/strong>typeof<\/strong> operator?<\/strong><\/h4>\n\n\n\n
<\/strong>typeof is used to check the type of a variable.<\/p>\n\n\n\n
\n\n\n\n<\/a>9. What are JavaScript functions?<\/strong><\/h4>\n\n\n\n
<\/strong>Functions are reusable blocks of code that perform a specific task.<\/p>\n\n\n\n\n
\n\n\n\n<\/a>10. What is an array in JavaScript?<\/strong><\/h4>\n\n\n\n
<\/strong>An array is a collection of items stored in a single variable.<\/p>\n\n\n\n\n
\n\n\n\n<\/a>11. What is an object in JavaScript?<\/strong><\/h4>\n\n\n\n
<\/strong>An object is a collection of key-value pairs.<\/p>\n\n\n\n\n
\n\n\n\n<\/a>12. What is the difference between <\/strong>for<\/strong> and <\/strong>while<\/strong> loops?<\/strong><\/h4>\n\n\n\n
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\n\n\n\n<\/a>13. What are JavaScript events?<\/strong><\/h4>\n\n\n\n
<\/strong>Events are actions that happen in the browser, like clicks, typing, or scrolling.<\/p>\n\n\n\n
\n\n\n\n<\/a>14. What is a callback function?<\/strong><\/h4>\n\n\n\n
<\/strong>A callback is a function passed as an argument to another function, to be executed later.<\/p>\n\n\n\n
\n\n\n\n<\/a>15. What is DOM in JavaScript?<\/strong><\/h4>\n\n\n\n
<\/strong>DOM (Document Object Model) represents the structure of a web page so JavaScript can interact with it.<\/p>\n\n\n\n
\n\n\n\n<\/a>16. What is an event listener?<\/strong><\/h4>\n\n\n\n
<\/strong>An event listener waits for a specific event (like a click) and then runs a function.<\/p>\n\n\n\n
\n\n\n\n<\/a>17. How do you create a variable in JavaScript?<\/strong><\/h4>\n\n\n\n
<\/strong>Use var, let, or const.<\/p>\n\n\n\n
\n\n\n\n<\/a>18. What is hoisting in JavaScript?<\/strong><\/h4>\n\n\n\n
<\/strong>Hoisting means moving variable and function declarations to the top of their scope before code execution.<\/p>\n\n\n\n
\n\n\n\n<\/a>19. What are template literals?<\/strong><\/h4>\n\n\n\n
<\/strong>Template literals allow you to embed variables and expressions in strings using backticks (`).<\/p>\n\n\n\n
\n\n\n\n<\/a>20. What is the difference between <\/strong>push<\/strong> and <\/strong>pop<\/strong> in arrays?<\/strong><\/h4>\n\n\n\n
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<\/a>Intermediate JavaScript Interview Questions and Answers<\/strong><\/h2>\n\n\n\n
\n\n\n\n<\/a>1. What is the difference between <\/strong>==<\/strong> and <\/strong>===<\/strong>?<\/strong><\/h4>\n\n\n\n
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\n\n\n\n<\/a>2. Explain closures in JavaScript.<\/strong><\/h4>\n\n\n\n
<\/strong>A closure is a function that remembers the environment in which it was created, even when it\u2019s executed outside of that environment.<\/p>\n\n\n\n
<\/strong>Closures are useful for data privacy, allowing functions to access variables even after the outer function has finished execution.<\/p>\n\n\n\n
\n\n\n\n<\/a>3. What is event bubbling in JavaScript?<\/strong><\/h4>\n\n\n\n
<\/strong>Event bubbling is a way in which events propagate through the DOM hierarchy. When an event is triggered on an element, it bubbles up to its parent elements, and so on, until it reaches the root.<\/p>\n\n\n\n
<\/strong>Event bubbling can be useful for event delegation, where you attach a single event listener to a parent element instead of individual child elements.<\/p>\n\n\n\n
\n\n\n\n<\/a>4. What is event delegation?<\/strong><\/h4>\n\n\n\n
<\/strong>Event delegation is a technique where you attach a single event listener to a parent element, rather than multiple listeners to each child element. This works because events bubble up the DOM.<\/p>\n\n\n\n
<\/strong>It\u2019s especially useful for handling dynamic elements added after the page load.<\/p>\n\n\n\n
\n\n\n\n<\/a>5. What are JavaScript Promises?<\/strong><\/h4>\n\n\n\n
<\/strong>A promise is an object representing the eventual completion or failure of an asynchronous operation. Promises help avoid callback hell and make async code more readable.<\/p>\n\n\n\n
<\/strong>Promises are often used with APIs or other operations that take time, such as fetching data from a server.<\/p>\n\n\n\n
\n\n\n\n<\/a>6. What is the difference between <\/strong>null<\/strong> and <\/strong>undefined<\/strong> in JavaScript?<\/strong><\/h4>\n\n\n\n
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