Front-end development is all about creating the visual and interactive aspects of a website that users see and interact with directly. Front-end developers need to be skilled in HTML, CSS, JavaScript, and various frameworks and tools. Interviewers assess both technical proficiency and understanding of user experience principles. The following Front End Developer Interview Questions and Answers cover key areas that will help you prepare for your next interview.
Q1. What is the difference between HTML and XHTML?
HTML is more lenient with errors and not case-sensitive, while XHTML is stricter, follows XML rules, and requires proper nesting and closing of tags.
Q2. What is the role of CSS in front-end development?
CSS controls the layout and appearance of web pages, including styling elements like fonts, colors, spacing, and responsiveness.
Q3. What is the difference between relative, absolute, and fixed positioning in CSS?
Relative positions an element relative to its normal position. Absolute positions it relative to its nearest positioned ancestor. Fixed positions it relative to the viewport.
Q4. What are media queries?
Media queries are CSS techniques used to apply styles based on screen size, resolution, and other device properties to create responsive layouts.
Q5. What are pseudo-elements in CSS?
Pseudo-elements allow styling specific parts of elements, such as ::before and ::after to insert content before or after an element’s content.
Q6. What is the difference between inline, block, and inline-block?
Inline does not break line and only takes necessary width. Block takes full width and breaks line. Inline-block behaves like inline but respects width and height.
Q7. What is the DOM?
DOM (Document Object Model) is a programming interface for HTML and XML documents, representing the structure as a tree of nodes that can be manipulated with JavaScript.
Q8. What is event bubbling?
Event bubbling is a process where events propagate from the innermost element to the outer elements in the DOM hierarchy.
Q9. How do you improve website performance?
Use minification, compress images, implement lazy loading, reduce HTTP requests, and use caching and CDNs.
Q10. What are some popular JavaScript frameworks?
React, Angular, Vue.js, and Svelte are commonly used frameworks and libraries for building dynamic front-end applications.
Q11. What is the difference between == and === in JavaScript?
== compares values after type conversion, whereas === compares both value and type without conversion.
Q12. What is hoisting in JavaScript?
Hoisting is JavaScript’s behavior of moving variable and function declarations to the top of their scope before execution.
Q13. What are closures?
Closures are functions that retain access to their lexical scope even when executed outside their original context.
Q14. What is a promise in JavaScript?
A promise represents the eventual result of an asynchronous operation. It can be pending, resolved, or rejected.
Q15. What are the differences between localStorage, sessionStorage, and cookies?
localStorage stores data with no expiration, sessionStorage stores data for the session, and cookies store small data with optional expiration and are sent with HTTP requests.
Q16. What is the difference between synchronous and asynchronous code?
Synchronous code blocks execution until tasks finish. Asynchronous code allows other operations while waiting for tasks to complete.
Q17. What is the difference between var, let, and const?
var is function-scoped and can be re-declared. let is block-scoped and cannot be re-declared. const is block-scoped and cannot be reassigned or re-declared.
Q18. What are arrow functions in JavaScript?
Arrow functions are a shorthand syntax for defining functions. They do not have their own bindings to this or arguments.
Q19. What is React?
React is a JavaScript library for building user interfaces. It allows the creation of reusable components and manages state efficiently with a virtual DOM.
Q20. What is the virtual DOM?
The virtual DOM is a lightweight copy of the real DOM used in libraries like React to improve performance by minimizing direct DOM manipulation.
Q21. How does React handle data flow?
React uses unidirectional data flow, where data is passed from parent to child components via props.
Q22. What are props in React?
Props are short for properties. They are read-only attributes used to pass data from one component to another in React.
Q23. What are states in React?
State is a built-in object that stores property values that belong to a component and may change over time.
Q24. What are React hooks?
Hooks are functions in React that let you use state and other features in functional components. Examples include useState and useEffect.
Q25. How do you optimize performance in a front-end application?
Use code-splitting, lazy loading, memoization, virtualized lists, and avoid unnecessary re-renders to improve performance.