Web Development Interview Questions for 3 Years Experience
40 questions with answers for candidates with 3 years of experience — 2 easy, 29 medium, 9 hard.
What interviewers expect: 3 years experience
Three-year candidates are judged on ownership. Expect questions on designing APIs, optimising slow queries with EXPLAIN, caching, secure authentication, deployment pipelines and handling production incidents. Interviewers also check how you review code and help juniors, and whether you can estimate tasks and explain trade-offs.
This set is weighted towards JavaScript Core (7), Web Security (6), MySQL Database (6), DOM and Browser Events (5).
Query optimisation API design CI/CD Code review
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When vertical margins of adjacent block elements touch, they merge into a single margin equal to the larger one instead of adding up. It also happens between a parent and its first or last child when no padding, border or block formatting context separates them. Margins do not collapse in flex or grid containers. Developers often avoid surprises by using padding, gap or margin in one direction only.
02
Write .htaccess rules to force HTTPS and the non-www domain.
On Apache with mod_rewrite enabled:
RewriteEngine On
RewriteCond %{HTTPS} off [OR]
RewriteCond %{HTTP_HOST} ^www\. [NC]
RewriteCond %{HTTP_HOST} ^(?:www\.)?(.+)$ [NC]
RewriteRule ^ https://%1%{REQUEST_URI} [L,R=301]
A 301 redirect tells search engines the change is permanent, so ranking signals move to one canonical URL. Test carefully, because a wrong rule can cause a redirect loop behind a proxy or load balancer.
03
What is the difference between a shallow copy and a deep copy?
A shallow copy, made with spread syntax or Object.assign, copies only top-level properties, so nested objects are still shared references. Changing copy.address.city also changes the original. A deep copy duplicates every nested level. Modern browsers and Node provide structuredClone(obj), which handles dates, maps and circular references. JSON.parse(JSON.stringify(obj)) also works but drops functions, undefined and converts dates to strings.
Set cookie parameters before session_start:
session_set_cookie_params([
'lifetime' => 0,
'path' => '/',
'secure' => true,
'httponly' => true,
'samesite' => 'Lax'
]);
ini_set('session.use_strict_mode', '1');
session_start();
secure sends the cookie only over HTTPS, httponly hides it from JavaScript so XSS cannot steal it, and SameSite reduces CSRF. Strict mode rejects session ids the server never created.
05
Your site suddenly shows 502 Bad Gateway. How do you troubleshoot it?
502 means Nginx could not get a valid response from the upstream, usually PHP-FPM or an application server. I would check if the service is running with systemctl status php8.3-fpm, read the Nginx error log and the PHP-FPM log, and confirm the socket path in the config matches. Common causes are crashed workers, exhausted pm.max_children, memory limits or a recent config change. Restarting brings it back, but the root cause must be fixed.
InnoDB is the default MySQL storage engine. It supports transactions, row-level locking, foreign keys and crash recovery, making it suitable for almost all applications. MyISAM uses table-level locking, has no transactions or foreign keys, and can corrupt on crashes. MyISAM was once faster for read-only workloads, but modern InnoDB matches or beats it. Old tables still on MyISAM should usually be converted.
07
Someone accidentally ran DELETE without a WHERE clause on production. How do you recover?
First I would stop writes to that table to avoid further damage and inform the team. Then I would restore the latest backup to a separate server and, if binary logging is enabled, replay binlog events up to just before the bad statement using mysqlbinlog for point-in-time recovery. Finally I would copy the recovered rows back. Afterwards I would enable safe-updates mode and restrict production access.
The Document Object Model is a tree representation of an HTML page that the browser builds after parsing. Each element, attribute and piece of text becomes a node that JavaScript can read and change through APIs like document.querySelector, element.classList and element.append. When the DOM changes, the browser updates what users see. The DOM is not the HTML source itself; scripts can change it after the page loads.
09
How do indexes work and when can they hurt performance?
InnoDB indexes are B+ trees that let MySQL find rows without scanning the whole table, which speeds up WHERE, JOIN and ORDER BY on indexed columns. A composite index follows the leftmost prefix rule. Indexes cost extra disk space and slow down INSERT, UPDATE and DELETE because each index must be updated. Low-selectivity columns like gender rarely benefit, and functions on columns in WHERE can stop index use.
Generate a token per session and compare it safely:
session_start();
if (empty($_SESSION['csrf'])) {
$_SESSION['csrf'] = bin2hex(random_bytes(32));
}
// in the form
echo "<input type='hidden' name='csrf' value='" . $_SESSION['csrf'] . "'>";
// on submit
if (!hash_equals($_SESSION['csrf'], $_POST['csrf'] ?? '')) {
http_response_code(403);
exit('Invalid request');
}
hash_equals compares in constant time, which avoids timing attacks.
11
Fetch data from an API with async/await and handle errors properly.
fetch only rejects on network failure, so check response.ok yourself:
async function getCourses() {
try {
const res = await fetch('/api/courses');
if (!res.ok) throw new Error('HTTP ' + res.status);
const data = await res.json();
renderCourses(data);
} catch (err) {
console.error(err);
showMessage('Could not load courses. Please retry.');
}
}
A 404 or 500 response would otherwise be treated as success.
12
Time to first byte is over 2 seconds even for simple pages. What do you check?
High TTFB points to the server, not the browser. I would check if OPcache is enabled, profile slow database queries, look for blocking external API calls during page generation, and check whether the server is low on CPU or memory. Fixes include full-page caching for anonymous users, object caching with Redis, upgrading PHP, choosing a server region close to Indian users, and putting a CDN in front.
PHP 8.0 added the JIT compiler, named arguments, union types, the match expression, the nullsafe operator ?-> and constructor property promotion. PHP 8.1 added enums, readonly properties, fibers and never return type. PHP 8.2 added readonly classes, 8.3 added typed class constants and json_validate, and 8.4 added property hooks and asymmetric visibility. Together they make PHP code safer, shorter and more strongly typed.
14
The page stutters while scrolling because of a scroll event handler. How do you fix it?
Scroll events fire many times per second, so heavy work in the handler blocks the main thread. I would throttle the handler or batch DOM writes inside requestAnimationFrame, mark listeners as { passive: true }, and avoid reading layout properties like offsetTop after writing styles. For tasks like lazy loading, sticky effects or reveal animations, I would replace the handler with IntersectionObserver or CSS position: sticky.
this depends on how a function is called, not where it is written. In a method call like user.greet(), this is user. In a plain function call it is undefined in strict mode. With new it is the new object, and call, apply or bind set it explicitly. Arrow functions do not have their own this; they take it from the surrounding scope, which is why they are handy inside callbacks.
16
What are data-* attributes and when do you use them?
Custom data attributes such as data-product-id or data-price let you store extra information on an element without misusing class or id. JavaScript reads them through element.dataset, for example button.dataset.productId, and CSS can target them with attribute selectors. They are ideal for passing small values from server-rendered HTML to scripts, but sensitive data should never be stored there because anyone can read the page source.
17
Tell me about a time you disagreed with a designer about a layout.
Situation: a designer wanted a five-column pricing table on mobile. Task: I had to deliver the design while keeping it usable on small screens. Action: I built a quick prototype on a real phone, showed that text became unreadable, and proposed a swipeable card version that kept the same visual style. Result: the designer agreed, we updated the Figma file together, and mobile conversions on that page improved after launch.
localStorage stores about 5 MB per origin and persists until cleared. sessionStorage has similar size but is cleared when the tab closes and is separate per tab. Cookies are small, around 4 KB, are sent to the server with every request, and can be HttpOnly, Secure and SameSite. Use cookies for session identifiers, and storage for UI preferences. Never store tokens or passwords in localStorage, since any XSS can read it.
19
Describe a bug you found in production and how you handled it.
Situation: after a release, users reported the checkout button did nothing on some phones. Task: I had to find and fix it quickly. Action: I reproduced it on an older Safari, found that a new array method was unsupported, rolled back the change, then added a polyfill and Babel targets for those browsers. Result: the fix shipped the same day, and we added real-device checks to our release checklist.
A many-to-many relationship needs a junction table:
CREATE TABLE students (
id INT AUTO_INCREMENT PRIMARY KEY,
name VARCHAR(100) NOT NULL,
email VARCHAR(150) NOT NULL UNIQUE
);
CREATE TABLE courses (
id INT AUTO_INCREMENT PRIMARY KEY,
title VARCHAR(150) NOT NULL
);
CREATE TABLE enrollments (
student_id INT,
course_id INT,
enrolled_on DATE NOT NULL,
PRIMARY KEY (student_id, course_id),
FOREIGN KEY (student_id) REFERENCES students(id) ON DELETE CASCADE,
FOREIGN KEY (course_id) REFERENCES courses(id)
);
22
How do arrow functions differ from regular functions?
Arrow functions have shorter syntax, an implicit return for single expressions, and no own this, arguments or super; they inherit these from the outer scope. They cannot be used as constructors with new and do not have a prototype property. This makes them ideal for callbacks like array.map, but unsuitable for object methods that need this to refer to the object, or for event handlers that rely on this as the element.
23
Your application logs show frequent deadlock errors. What do you do?
A deadlock happens when two transactions each hold a lock the other needs; InnoDB kills one. I would read SHOW ENGINE INNODB STATUS to see the conflicting queries. Fixes include accessing tables and rows in a consistent order, keeping transactions short, adding indexes so updates lock fewer rows, and avoiding user interaction inside a transaction. The application should also retry the failed transaction once or twice.
Never store plain text or use md5 or sha1, which are fast and easily cracked. Use password_hash($password, PASSWORD_DEFAULT), which currently uses bcrypt with an automatic random salt, or PASSWORD_ARGON2ID where available. At login use password_verify($input, $hash). password_needs_rehash lets you upgrade old hashes when the default algorithm or cost changes. The hash column should be VARCHAR(255) to allow future algorithms.
25
Limit failed login attempts to stop brute-force attacks.
Track failures per account and IP, then block temporarily:
$stmt = $pdo->prepare('SELECT COUNT(*) FROM login_attempts
WHERE ip = ? AND attempted_at > NOW() - INTERVAL 15 MINUTE');
$stmt->execute([$_SERVER['REMOTE_ADDR']]);
if ($stmt->fetchColumn() >= 5) {
http_response_code(429);
exit('Too many attempts. Try again in 15 minutes.');
}
// on failure
$pdo->prepare('INSERT INTO login_attempts (ip, attempted_at) VALUES (?, NOW())')
->execute([$_SERVER['REMOTE_ADDR']]);
Add CAPTCHA after a few failures and offer two-factor authentication.
An iterator is an object with a next() method returning { value, done }, and any object with a Symbol.iterator method can be used in for...of loops and spread syntax. A generator function, written function*, creates iterators easily: each yield pauses execution and returns a value, resuming on the next call. Generators are useful for lazy sequences, such as paginated API results, without building huge arrays in memory.
27
Your frontend on one domain gets a CORS error calling your API on another. How do you resolve it?
The fix belongs on the API server, not the frontend. I would configure it to return Access-Control-Allow-Origin with the exact frontend origin, handle OPTIONS preflight requests with the allowed methods and headers, and add Access-Control-Allow-Credentials: true if cookies are needed. Alternatively, serving the API under the same domain through a reverse proxy, like /api, removes cross-origin calls altogether.
28
How do you manage configuration and secrets across local, staging and production?
I keep code identical across environments and change only configuration through environment variables, usually loaded from a .env file that is never committed. A .env.example documents required keys without values. In production, secrets live in the server environment, the CI secret store or a cloud secrets manager. Each environment has separate database credentials and API keys, so a staging leak cannot affect production.
29
Explain database normalization up to third normal form.
Normalization reduces duplicate data and update problems. 1NF requires atomic values, no repeating groups like phone1, phone2. 2NF requires every non-key column to depend on the whole primary key, not part of a composite key. 3NF removes transitive dependencies, so a column depends only on the key, for example moving city details out of an orders table. Read-heavy reports sometimes denormalise deliberately for speed.
30
Use the picture element to serve WebP or AVIF with a JPEG fallback.
The browser picks the first source format it supports and falls back to img:
<picture>
<source srcset='hero.avif' type='image/avif'>
<source srcset='hero.webp' type='image/webp'>
<img src='hero.jpg' alt='Students in a coding lab' width='1200' height='600'>
</picture>
The img element still carries alt, width and height, so accessibility and layout stability are preserved. Modern formats are often 30 to 50 percent smaller than JPEG.
Cross-site request forgery tricks a logged-in user's browser into sending an unwanted request, such as changing their email, because cookies are attached automatically. Prevention includes a unique CSRF token in every state-changing form that the server verifies, SameSite=Lax or Strict cookies, and checking the Origin header. GET requests should never change data. Frameworks like Laravel add CSRF tokens to forms by default.
32
Tell me about a time you had to work with messy legacy code.
Situation: I joined a project with a 10-year-old PHP codebase full of mixed HTML and SQL. Task: I needed to add online payments without breaking existing features. Action: I wrote tests around the checkout flow first, extracted database code into a small class using PDO, and added the payment module separately. Result: payments launched with no regressions, and the team adopted the same approach for later changes.
33
What are CSS custom properties and how are they different from Sass variables?
Custom properties like --brand: #2563eb are defined in CSS and read with var(--brand). They cascade, can be changed per element or media query, and can be updated at runtime with JavaScript, which makes themes and dark mode easy. Sass variables are replaced at compile time and do not exist in the browser. Many teams use both: Sass for build-time logic and custom properties for runtime theming.
34
How would you explain a technical problem to a non-technical client?
Situation: a client asked why their site was slow on mobile. Task: I needed approval to optimise images, which meant extra work. Action: I avoided jargon, showed a side-by-side video of load times, and compared large images to sending a heavy parcel by post. Result: the client approved the work, load time dropped from 7 to 2.5 seconds, and they trusted my later suggestions more.
35
A third-party widget's CSS keeps overriding your button styles. How do you handle it?
First I would check which selector wins in DevTools and why. Options include scoping my styles with a more specific component class, using CSS cascade layers so third-party CSS sits in a lower layer, or loading the widget inside an iframe or Shadow DOM so its styles are isolated. I would avoid adding !important everywhere, because it starts an override war that becomes impossible to maintain.
36
Validate a signup form with JavaScript before submission.
Check fields on submit and show inline messages:
form.addEventListener('submit', (e) => {
const errors = [];
if (form.name.value.trim().length < 3) errors.push('Name too short');
if (!/^[6-9]\d{9}$/.test(form.mobile.value)) errors.push('Invalid mobile');
if (form.password.value !== form.confirm.value) errors.push('Passwords do not match');
if (errors.length) {
e.preventDefault();
errorBox.textContent = errors.join('. ');
}
});
Client validation improves experience, but the server must validate again.
37
Users report being redirected to a gambling site from your pages. What do you check?
This often comes from injected JavaScript or a compromised third-party script. I would check the page source and Network tab for unfamiliar scripts, inspect .htaccess for malicious rewrite rules, search the database and theme files for obfuscated code like base64_decode or eval, and review recently changed files on the server. A strict CSP and Subresource Integrity on CDN scripts help prevent repeat incidents.
Every object has an internal link to another object called its prototype. When a property is not found on the object, JavaScript looks up the prototype chain until it reaches Object.prototype and then null. Class syntax is a cleaner layer over this model: class Admin extends User sets Admin.prototype to inherit from User.prototype. Methods defined on the prototype are shared across instances, which saves memory.
39
How do srcset and sizes help with responsive images?
srcset lists several versions of the same image with their widths, for example hero-480.jpg 480w and hero-1200.jpg 1200w. sizes tells the browser how wide the image will be shown at different viewport widths. The browser then picks the smallest file that still looks sharp for that screen and pixel density. This saves a lot of mobile data compared to sending one large image to every device.
40
What is the difference between an abstract class and an interface in PHP?
An interface defines only method signatures and constants, and a class can implement many interfaces. An abstract class can contain properties, constructors and implemented methods along with abstract ones, but a class can extend only one. Use an interface to define a contract like PaymentGateway, and an abstract class to share common code among closely related classes, such as a base Controller.
Frequently asked questions
What is asked in Web Development interviews for 3 years of experience?
Three-year candidates are judged on ownership. Expect questions on designing APIs, optimising slow queries with EXPLAIN, caching, secure authentication, deployment pipelines and handling production incidents. Interviewers also check how you review code and help juniors, and whether you can estimate tasks and explain trade-offs.
How many questions should I practise before a Web Development interview?
Work through all 40 questions here, then the company-wise sets for the employers you are targeting. Quality matters more than count: be able to explain why each answer is right.
Which topics matter most for 3 years of experience?
Focus first on Query optimisation, API design, CI/CD, Code review.