Basic Questions
Q1: What is JavaScript?
A programming language that adds dynamic behavior to websites.
Q2: Difference between let, var, and const?
var is function-scoped, let/const are block-scoped; const cannot be reassigned.
Q3: What is a function in JavaScript?
A block of code that performs a task when called.
Q4: What is an array?
A list-like object to store multiple values in one variable.
Q5: How to declare an object?
let obj = { name: 'John', age: 30 };
Q6: How to get element by ID in JS?
Use document.getElementById('id').
Q7: What is an event in JavaScript?
A user action like click, hover, submit, etc., that triggers a response.
Q8: How to convert JSON string to JS object?
Use JSON.parse(string).
Q9: What does setTimeout() do?
Delays code execution by a given number of milliseconds.
Q10: What is typeof operator?
Returns the data type of a variable (e.g., string, number).
Mid Level Questions
Q1: What is the DOM?
Document Object Model : allows JavaScript to manipulate HTML elements.
Q2: What is addEventListener()?
A method to attach event handlers to DOM elements.
Q3: What is a callback function?
A function passed as a parameter to be executed later.
Q4: Difference between == and ===?
== compares value (type-coerced), === checks value & type strictly.
Q5: What is a Promise in JS?
An object representing the eventual result of an async operation.
Q6: What is async/await?
Syntax that makes handling Promises easier and more readable.
Q7: What is localStorage?
Stores data in the browser permanently (until manually cleared).
Q8: What is NaN in JavaScript?
Stands for 'Not a Number', returned for invalid numeric operations.
Q9: Difference between null and undefined?
null is intentional no value; undefined means no value assigned.
Q10: Difference between forEach() and map()?
forEach() loops without return. map() returns a new array after transformation.