Preparing for a web developer interview in 2025 means being ready to answer questions that cover many areas, from general web concepts to specific HTML5, CSS, and JavaScript topics. Candidates should know about persistent storage options like localStorage and cookies, and understand standards bodies such as W3C. It’s also important to discuss performance optimization techniques like browser caching and image compression. In HTML5 part, familiarity with new elements like <article> or APIs is expected. CSS knowledge includes box model basics, selectors, and media queries for responsiveness. For JavaScript, understanding event bubbling, closures, and type conversions will help greatly. Overall, these questions reflect current industry needs without overcomplication.
Table of Contents
- General Web Developer Interview Questions
- HTML and HTML5 Interview Questions
- CSS Interview Questions
- JavaScript Interview Questions
- Frequently Asked Questions
General Web Developer Interview Questions
Persistent storage in browsers allows web applications to save data on the client side. The main options are localStorage, sessionStorage, and cookies. localStorage stores data with no expiration, making it useful for long-term data retention. sessionStorage keeps data only for the duration of the page session, so it’s cleared when the tab closes. Cookies are smaller, sent with every HTTP request, and often used for authentication or tracking, but they have size limits and security considerations.
The W3C, or World Wide Web Consortium, is the main international body that develops web standards to ensure consistent and accessible web experiences across browsers. It produces recommendations for HTML, CSS, and other web technologies, helping browsers interpret code uniformly.
Reducing web application load time is critical. Common techniques include enabling browser caching to reuse resources, optimizing images by compressing them without quality loss, minimizing HTTP requests by combining files or using inline assets, and reducing redirects to avoid extra server trips.
Graceful degradation is a design approach where a website is built with advanced features but still works acceptably in older or less capable browsers. This ensures basic functionality remains even if some modern features are unsupported.
A Document Type Declaration (DTD) is a line at the top of an HTML document that tells browsers which HTML version to expect. It helps browsers render pages correctly and avoid falling into quirks mode, which can cause inconsistent layouts.
Web design focuses on the look and feel of a website, including layout, colors, and user interface. Web development covers the broader process of building the site, including coding, functionality, testing, and deployment.
Cross-Origin Resource Sharing (CORS) is a security feature that controls how resources from one domain can be requested by another. It uses headers to specify which domains are allowed to access resources, preventing unauthorized cross-site requests.
HTTP/2 offers performance improvements over HTTP 1.1 by allowing multiple requests and responses simultaneously over a single connection (multiplexing), compressing headers to reduce overhead, prioritizing important resources, and enabling server push to send assets proactively.
Optimizing website assets involves combining files (concatenation) to reduce the number of requests, compressing files with gzip or Brotli to lower file size, and using Content Delivery Networks (CDNs) to serve assets from servers closer to users, reducing latency.
Browsers use standards mode or quirks mode to render pages. Standards mode follows W3C specifications strictly, leading to consistent behavior. Quirks mode mimics older browser bugs for compatibility with legacy sites but can cause inconsistent rendering and layout issues.
| Storage Type | Persistence | Size Limit | Accessibility | Use Case |
|---|---|---|---|---|
| Cookies | Persistent but can be set to expire | ~4KB | Sent with every HTTP request | Tracking, session management |
| localStorage | Persistent until explicitly cleared | 5-10MB | Accessible only via JavaScript in same origin | Storing large data locally, offline capabilities |
| sessionStorage | Cleared when tab or window closes | 5-10MB | Accessible only via JavaScript in same origin and session | Temporary data storage during a single session |
HTML and HTML5 Interview Questions
HTML, or HyperText Markup Language, is the fundamental language used to create web pages. Its purpose is to structure content on the web, allowing browsers to render text, images, links, and other media. In HTML, tags are the markup used to define elements. For example, <p> is a tag, and <p>This is a paragraph</p> is an element where the tag surrounds the content to give it meaning and structure.
The DOCTYPE declaration at the top of an HTML document tells the browser which version of HTML to expect. It helps browsers decide whether to render the page in standards mode or quirks mode; standards mode follows W3C rules strictly, while quirks mode tries to emulate old browser behaviors for legacy sites.
Serving XHTML pages can be tricky because many browsers, especially older versions of Internet Explorer, do not fully support XHTML’s XML parsing rules. This can lead to compatibility issues, so XHTML is less common in modern web development.
In HTML, bulleted lists use the <ul> tag with list items <li>, while numbered lists use <ol> with <li>. For example, <ul><li>Item 1</li></ul> creates a bulleted list, and <ol><li>Item 1</li></ol> creates a numbered list.
The <div> element is a generic container used to group other elements for styling or scripting. In contrast, the <frame> element, which split the browser window into multiple sections, is deprecated due to usability and SEO issues. Modern alternatives include <iframe> for embedding external content and CSS layouts (like Flexbox or Grid) for page structure.
HTML5 brought many improvements over HTML. Key differences include the introduction of new semantic elements, enhanced multimedia support without plugins, offline capabilities, and powerful JavaScript APIs. Semantic elements like <article>, <section>, and <nav> give meaning to page parts, improving accessibility and SEO. For example, <nav> defines navigation links, <article> represents standalone content, and <section> groups related content.
HTML5 also includes the <canvas> element, which allows for drawing graphics via scripting, useful for games or visualizations. WebGL builds on <canvas> to enable 3D graphics in the browser.
Another feature is data attributes, which let developers embed custom data inside elements using attributes like data-user-id="123". These attributes can be accessed through JavaScript, allowing dynamic behavior without cluttering standard attributes.
CSS Interview Questions
There are three common ways to apply CSS styles: external, internal, and inline. External CSS uses a separate stylesheet linked via the <link> tag, which keeps styles organized and reusable across multiple pages but requires an additional HTTP request. Internal CSS is written inside a <style> tag within the HTML <head>, useful for page-specific styles but can bloat the HTML file. Inline CSS applies styles directly to an element with the style attribute, offering quick, targeted changes but leads to poor maintainability and overrides other styles.
The CSS box model is fundamental to layout and spacing. It consists of four parts: content (the actual text or image), padding (space between content and border), border (the line surrounding padding), and margin (space outside the border that separates elements). Understanding how these layers interact helps control element size and spacing precisely.
Inline elements only take up as much width as their content and do not start on a new line, like <span> or <a>. Block elements, such as <div> or <p>, take the full width available and start on a new line, affecting the flow by stacking vertically. This difference impacts layout and how elements are arranged on the page.
Grouping selectors in CSS allow multiple selectors to share the same style rule by separating them with commas, for example, h1, h2, h3 { color: blue; }. This simplifies the CSS by avoiding repetition and keeps the code cleaner.
Class selectors and ID selectors differ mainly in specificity and usage. Classes, prefixed with a dot (.className), can be applied to multiple elements, making them flexible for styling groups. IDs, prefixed with a hash (#idName), must be unique within a page and have higher specificity, so they override class styles when both apply.
The difference between visibility: hidden and display: none is important for layout. visibility: hidden hides the element but keeps its space reserved in the layout, so surrounding elements don’t shift. display: none removes the element entirely from the layout flow, causing other elements to fill the space.
CSS preprocessors like SASS and LESS extend CSS by supporting variables, nesting, mixins, and functions, which help write more maintainable and scalable stylesheets. They compile down to regular CSS that browsers understand.
Child selectors target direct descendants of an element using the > symbol. For example, ul > li selects only the immediate <li> children of a <ul>, not nested <li> elements further down the tree.
CSS grid systems provide a powerful way to create responsive layouts by dividing a page into rows and columns. They allow precise control over element placement both horizontally and vertically, adapting easily to different screen sizes.
Using shorthand CSS properties helps write cleaner and more efficient code. For instance, instead of writing separate rules for each margin side (margin-top, margin-right, etc.), you can use margin: 10px 5px; to set vertical and horizontal margins at once, reducing code size and improving readability.
- External CSS: stored in separate .css files and linked to HTML, allows reuse and separates content from design
- Internal CSS: written within