JavaScript Interview Questions

JavaScript Interview Questions

1. What is JavaScript?

JavaScript is a versatile programming language primarily used for creating interactive web pages. It adds animation, dynamic content, and user responsiveness to websites.

2. What are the different data types in JavaScript?

There are various data types including:

  • String: “Hello World!”
  • Number: 123, 3.14
  • Boolean: true, false
  • Object: collections of key-value pairs
  • Array:¬†an ordered list of values

3. What are variables and how do you declare them?

Variables store data in your program. You declare a variable with the “let” or “const” keyword followed by its name and assignment (if any).

4. What are functions and how do you define them?

Functions are reusable blocks of code that perform specific tasks. You define a function with the “function” keyword followed by its name, parameters (inputs), and code block.

5. What is the difference between let and const?

  • let: re-assignable variable
  • const: value cannot be changed after it’s assigned

6. What is DOM and how does it interact with JavaScript?

DOM (Document Object Model) is the representation of a web page as a tree structure. JavaScript can manipulate the DOM to change element styles, content, and behavior.

7. What are events and how are they handled in JavaScript?

Events are user interactions or browser activities (e.g., clicking a button). JavaScript code can be attached to events to react and perform specific actions.

8. What is the purpose of conditional statements and what are some common ones?

Conditional statements control the flow of your code based on a given condition. Examples include:

  • if statement: executes code if a condition is true
  • else statement: executes code if a condition is false
  • switch statement: chooses different code blocks based on multiple conditions

9. What are arrays and how can you access elements within them?

Arrays are ordered lists of values. You can access elements by their index (position) starting from 0.

10. What are some best practices for writing clean and readable JavaScript code?

  • Use meaningful variable names.
  • Follow consistent indentation.
  • Add comments to explain your code.
  • Avoid unnecessary complexity.