If you are preparing for a web development job, learning javascript interview questions and answers is very important. JavaScript is one of the most used programming languages in the world. Almost every website uses it to create interactive features like buttons, forms, animations, and more.
Whether you are a student, beginner, working professional, or someone switching careers, this guide will help you understand important javascript interview questions, basic concepts, and real examples in a very simple way.
Let’s start learning step by step.
Basic JavaScript Interview Questions
1. What is JavaScript?
JavaScript is a programming language used to make websites interactive.
Example: Clicking a button and showing a message.
2. What are the features of JavaScript?
Easy to learn
Runs in the browser
Fast execution
Supports event handling
Works with HTML and CSS
3. What is a variable in JavaScript?
A variable is used to store data.
Example:
let name = "Kamal";4. Difference between var, let, and const?
var: Old way, function scope
let: Block scope, can change value
const: Block scope, cannot change value
5. What are data types in JavaScript?
String
Number
Boolean
Undefined
Null
Object
JavaScript Functions and Scope
6. What is a function?
A function is a block of code that performs a task.
7. What is function scope?
Scope means where a variable can be used.
8. What is a closure?
A closure allows a function to access variables from another function.
Real-life example:
Like remembering your login details even after refreshing the page.
9. What is an arrow function?
A shorter way to write a function.
const add = (a, b) => a + b;10. What is hoisting?
JavaScript moves variables and functions to the top before execution.
JavaScript DOM Questions
11. What is DOM?
DOM means Document Object Model. It allows JavaScript to change HTML content.
12. How to select elements in JavaScript?
getElementById
querySelector
13. What is event handling?
Event handling means responding to user actions like clicks.
14. What is addEventListener?
It is used to handle events.
button.addEventListener("click", function(){});15. What is innerHTML?
Used to change content inside HTML.
Intermediate JavaScript Interview Questions
16. What is an array?
An array stores multiple values.
let fruits = ["apple", "banana"];17. What is an object?
An object stores data in key-value form.
18. Difference between and =?
== checks value
=== checks value and type
19. What is NaN?
It means “Not a Number”.
20. What is undefined?
A variable declared but not assigned a value.
21. What is null?
A variable with no value intentionally.
22. What is a loop?
Used to repeat code.
23. Types of loops?
for
while
do-while
24. What is break and continue?
break stops loop
continue skips one step
25. What is a callback function?
A function passed into another function.
Advanced JavaScript Interview Questions
26. What is promise?
Used to handle async operations.
27. What are async and await?
Used to write cleaner async code.
28. What is event bubbling?
Event goes from child to parent.
29. What is event capturing?
Event goes from parent to child.
30. What is JSON?
JavaScript Object Notation used to store data.
31. What is localStorage?
Used to store data in browser.
32. What is sessionStorage?
Stores data for one session.
33. What is API?
API connects frontend and backend.
34. What is fetch()?
Used to get data from API.
35. What is debouncing?
Limits function calls.
36. What is throttling?
Controls how often a function runs.
37. What is prototype?
Used for inheritance.
38. What is class in JavaScript?
Blueprint for objects.
39. What is inheritance?
One object using another object’s properties.
40. What is ES6?
New version of JavaScript with features like arrow functions and classes.
41. What is spread operator?
Used to copy data.
let arr2 = [...arr1];42. What is destructuring?
Extract values from arrays or objects.
43. What is map() method?
Used to transform array.
44. What is filter() method?
Used to filter data.
45. What is reduce() method?
Used to combine values.
46. What is setTimeout()?
Runs code after delay.
47. What is setInterval()?
Runs code repeatedly.
Tips to Crack JavaScript Interview
Practice daily coding
Understand basics clearly
Build small projects
Learn real examples
Revise important concepts
Benefits of Learning JavaScript
High demand skill
Good salary opportunities
Works in frontend and backend
Many job roles available
FAQs
What are common javascript interview questions?
They include variables, functions, DOM, promises, and arrays.
How to prepare for javascript interview questions and answers?
Practice coding, revise basics, and solve real examples.
Are javascript basic interview questions enough?
Yes, for freshers. For experienced roles, advanced topics are also needed.
How important is JavaScript for jobs?
Very important. Most companies require JavaScript skills.
Conclusion
JavaScript is one of the most important skills in today’s tech world. By learning these javascript interview questions and answers, you can build strong basics and feel confident in interviews. Practice regularly, understand concepts clearly, and work on real projects to improve your skills.
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