Top 25 Interview Q&A -JavaScript, PHP, MySQL & WordPress Customization

In today’s web development ecosystem, employers look for professionals who can seamlessly work across front-end scripting, server-side logic, databases, and CMS customization. JavaScript, PHP, MySQL, and WordPress together form a powerful and widely used full-stack combination.

This blog covers the Top 25 most frequently asked interview questions with clear, practical answers, helping you crack interviews for Web Developer, WordPress Developer, PHP Developer, and Full-Stack roles.

1. What is JavaScript and why is it important?

JavaScript is a client-side scripting language used to create dynamic and interactive web pages. It allows developers to handle events, validate forms, manipulate the DOM, and communicate with servers using AJAX or APIs. Today, JavaScript is also used on the server side through Node.js, making it a full-stack language.

2. What is the difference between var, let, and const?

• var: Function-scoped, can be redeclared, causes hoisting issues
• let: Block-scoped, cannot be redeclared
• const: Block-scoped, value cannot be reassigned

Best practice is to use let and const to avoid unexpected bugs.

3. What is the DOM?

The Document Object Model (DOM) is a programming interface that represents HTML as a tree structure. JavaScript uses the DOM to dynamically change content, styles, and structure of a webpage without reloading it.

4. What is event bubbling?

Event bubbling means that an event triggered on a child element propagates upward to its parent elements. JavaScript allows control over this behavior using event.stopPropagation().

5. What are closures in JavaScript?

A closure is a function that remembers variables from its outer scope even after the outer function has executed. Closures are commonly used for data privacy and function factories.

6. What is JSON?

JSON (JavaScript Object Notation) is a lightweight data interchange format used for sending data between client and server. It is easy to read, write, and parse.

7. What is AJAX?

AJAX (Asynchronous JavaScript and XML) allows web pages to fetch data from the server without reloading the page, improving user experience and performance.

8. What is PHP?

PHP is a server-side scripting language used to build dynamic websites and web applications. It is widely used with CMS platforms like WordPress and frameworks such as Laravel.

9. What is the difference between echo and print?

• echo: Faster, can output multiple strings
• print: Returns a value (1), slightly slower

Both are used to display output in PHP.

10. What are PHP sessions and cookies?

• Cookies store data on the client’s browser
• Sessions store data on the server

Sessions are more secure and commonly used for authentication.

11. What is the difference between include and require?

• include: Shows a warning if file is missing
• require: Stops script execution if file is missing

Use require for critical files.

12. What is PDO in PHP?

PDO (PHP Data Objects) is a secure database access layer that supports prepared statements, preventing SQL injection attacks.

13. What are prepared statements?

Prepared statements separate SQL logic from data, improving security and performance when executing database queries multiple times.

14. What is PHP error handling?

PHP supports error handling using try, catch, custom error handlers, and logging errors to files instead of displaying them to users.

15. What is MySQL?

MySQL is an open-source relational database management system (RDBMS) used to store structured data for web applications.

16. What is the difference between DELETE, TRUNCATE, and DROP?

• DELETE: Removes specific rows
• TRUNCATE: Removes all rows quickly
• DROP: Deletes the entire table structure

17. What are primary and foreign keys?

• Primary Key uniquely identifies a record
• Foreign Key links two tables together

They ensure data integrity.

18. What is normalization?

Normalization is the process of organizing data to reduce redundancy and improve data consistency by dividing tables logically.

19. What is indexing?

Indexing improves query performance by allowing faster data retrieval, similar to an index in a book.

20. What is WordPress?

WordPress is an open-source content management system (CMS) built using PHP and MySQL. It is used for blogs, websites, and eCommerce stores.

21. What are themes and plugins?

• Themes control design and layout
• Plugins add functionality

Custom development often involves modifying both.

22. What is a child theme?

A child theme inherits functionality from a parent theme and allows safe customization without losing changes during updates.

23. What are hooks in WordPress?

Hooks allow developers to modify WordPress behavior without changing core files.

• Actions execute custom code
• Filters modify data

24. How do you create a custom plugin?

A custom plugin is created by:

1. Creating a folder in /wp-content/plugins
2. Adding a PHP file with plugin header
3. Writing custom functionality using hooks

25. How do you optimize WordPress performance?

• Use caching plugins
• Optimize images
• Use a CDN
• Minimize plugins
• Optimize database queries

Conclusion

Mastering JavaScript, PHP, MySQL, and WordPress Customization gives you a strong advantage in full-stack and CMS-based development roles. These 25 interview questions and answers cover both theoretical concepts and practical knowledge, making them ideal for interviews in web development agencies, startups, and enterprises.

If you are preparing for interviews, revise these questions, practice coding examples, and build small projects to strengthen your confidence.