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Web Development Telephonic Interview Questions & Answers

30 questions for the telephonic interview stage — 17 easy, 13 medium.

About the telephonic interview round

The telephonic or screening round is a 15-30 minute call with a recruiter or engineer. It checks your basics, your CV and whether you can explain Web Development concepts clearly without a screen to point at.

Tips for the telephonic interview round

  • Keep your CV in front of you and be ready to explain every line on it.
  • Answer in short, clear sentences; there is no whiteboard, so structure matters.
  • Take the call somewhere quiet and confirm the time in advance.
  • Prepare one question to ask the interviewer at the end.
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01

What is the difference between == and ===?

JavaScript CoreEasy
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== compares values after type coercion, so 0 == '0' and null == undefined are both true, which can hide bugs. === is strict equality and returns true only when both type and value match, so 0 === '0' is false. Most style guides require === everywhere. One accepted exception is value == null, which conveniently checks for both null and undefined in one condition.
02

What is a CDN and how does it improve a website?

Hosting and DeploymentMedium
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A content delivery network caches static files such as images, CSS and JavaScript on servers in many locations, so a user in Chennai is served from a nearby edge rather than a distant origin. This reduces latency, lowers load on your server and absorbs traffic spikes and some DDoS attacks. Cache-Control headers decide how long files stay cached, and versioned filenames let you deploy updates without stale content.
03

What is the difference between block-level and inline elements?

HTML FundamentalsEasy
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Block-level elements such as div, p, h1 and section start on a new line and take the full available width by default. Inline elements such as span, a, strong and img sit inside a line of text and only take as much width as their content. Inline elements ignore vertical width and height settings, which is why developers often switch them to inline-block or block when they need sizing.
04

What is the difference between UNION and UNION ALL?

MySQL DatabaseEasy
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Both combine the results of two SELECT queries with the same number and type of columns. UNION removes duplicate rows, which requires extra sorting or hashing work. UNION ALL keeps all rows, including duplicates, and is therefore faster. Use UNION ALL when you know results cannot overlap or duplicates are acceptable, for example combining this year's and last year's order tables.
05

Compare localStorage, sessionStorage and cookies.

DOM and Browser EventsMedium
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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.
06

Name important features added in PHP 8.x.

PHP ProgrammingMedium
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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.
07

What is margin collapsing?

CSS Layout and Responsive DesignMedium
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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.
08

Explain the common DNS record types.

Hosting and DeploymentEasy
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An A record maps a domain to an IPv4 address and AAAA to IPv6. CNAME points one name to another, such as www to example.com, but cannot sit on the root domain. MX records route email to mail servers. TXT records hold verification and email security data like SPF, DKIM and DMARC. NS records name the authoritative nameservers. TTL controls how long resolvers cache each record.
09

What is the difference between echo and print in PHP?

PHP ProgrammingEasy
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Both output strings. echo is a language construct with no return value and can take multiple comma-separated arguments, like echo $a, $b. print also is a construct but takes only one argument and returns 1, so it can be used inside expressions. echo is marginally faster and far more common. For formatted output, printf or sprintf are used, for example printf('%.2f', $price).
10

A client wants better Google rankings. What HTML-level changes would you make?

HTML FundamentalsMedium
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I would give every page a unique title and meta description, use exactly one clear h1 with a logical h2 and h3 structure, and add descriptive alt text. I would add canonical tags to avoid duplicate content, structured data such as JSON-LD for courses or FAQs, and internal links with meaningful anchor text. I would also improve Core Web Vitals, since page speed affects ranking.
11

What are PHP superglobals?

PHP ProgrammingEasy
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Superglobals are built-in arrays available in every scope without the global keyword. Common ones are $_GET and $_POST for request data, $_REQUEST combining them, $_SESSION, $_COOKIE, $_FILES for uploads, $_SERVER for headers and paths, and $_ENV for environment variables. All user-supplied superglobals must be treated as untrusted input and validated, for example using filter_input(INPUT_POST, 'email', FILTER_VALIDATE_EMAIL).
12

How do you keep yourself updated with changes in web standards?

HTML FundamentalsMedium
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I follow MDN Web Docs, web.dev and the release notes of Chrome and Firefox, and I check Can I Use before adopting a new feature. Every few weeks I build a small demo with something new, such as container queries or the popover attribute, and push it to GitHub. For example, after reading about native lazy loading, I replaced a JavaScript library in my project and reduced the bundle size.
13

Limit failed login attempts to stop brute-force attacks.

Web SecurityMedium
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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.
14

What is the difference between var, let and const?

JavaScript CoreEasy
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var is function-scoped, is hoisted and initialised as undefined, and can be redeclared, which causes bugs in loops and blocks. let and const are block-scoped and sit in the temporal dead zone until their declaration line runs. let allows reassignment, while const does not, although objects declared with const can still have their properties changed. Modern code uses const by default and let only when the value must change.
15

What is the DOM?

DOM and Browser EventsEasy
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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.
16

What is event delegation and why is it useful?

DOM and Browser EventsMedium
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Event delegation attaches one listener to a common parent instead of many listeners on child elements, then uses event.target.closest() to find which child was clicked. Because of bubbling, it works even for children added later. For example, one listener on a ul can handle delete buttons for hundreds of todo items. It saves memory and avoids re-binding listeners after dynamic updates.
17

Why should external links opened with target='_blank' use rel='noopener'?

HTML FundamentalsEasy
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When a page opens a link in a new tab, the new page historically got access to window.opener and could redirect the original tab to a phishing page, an attack called reverse tabnabbing. Adding rel='noopener' removes that reference, and noreferrer also hides the referring URL. Modern browsers apply noopener by default for target='_blank', but adding it explicitly is still good practice for older browsers.
18

What is the difference between GET and POST methods in an HTML form?

HTML FundamentalsEasy
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GET sends form data in the URL query string, so it is visible, bookmarkable, cached and limited in length; it suits search and filter forms. POST sends data in the request body, so it is not shown in the URL and can carry large or binary content such as file uploads. Any action that changes data on the server, like login, registration or payment, should use POST.
19

What are truthy and falsy values?

JavaScript CoreEasy
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In a boolean context, JavaScript converts values to true or false. The falsy values are false, 0, -0, 0n, empty string, null, undefined and NaN; everything else is truthy, including '0', empty arrays and empty objects. This matters in conditions: if (items.length) works, but if (count) fails when count is legitimately 0. The nullish coalescing operator ?? helps by only falling back for null or undefined.
20

How is querySelector different from getElementById and getElementsByClassName?

DOM and Browser EventsEasy
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querySelector and querySelectorAll accept any CSS selector and return the first match or a static NodeList. getElementById accepts only an id and is slightly faster. getElementsByClassName returns a live HTMLCollection that updates automatically when the DOM changes, which can cause surprises inside loops. In practice querySelector is used for flexibility, and the speed difference rarely matters.
21

What is SQL injection and how do prepared statements stop it?

Web SecurityEasy
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SQL injection happens when user input is concatenated into a query, so input like ' OR '1'='1 changes the query's logic and can dump or delete data. Prepared statements send the SQL structure and the data separately, so the database always treats input as a value, never as code. Escaping functions are not a full substitute. Least-privilege database users limit the damage if a flaw slips through.
22

Why is the meta viewport tag needed for mobile pages?

HTML FundamentalsMedium
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Without a viewport meta tag, mobile browsers render the page at a virtual width of around 980 pixels and then zoom out, so text looks tiny. Adding <meta name='viewport' content='width=device-width, initial-scale=1'> tells the browser to use the real device width, which makes media queries work as expected. Avoid disabling user zoom with maximum-scale=1 because it hurts accessibility for users with low vision.
23

What is the difference between WHERE and HAVING?

MySQL DatabaseEasy
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WHERE filters individual rows before grouping and cannot use aggregate functions. HAVING filters groups after GROUP BY and can use aggregates. For example, SELECT city, COUNT(*) FROM students WHERE status = 'active' GROUP BY city HAVING COUNT(*) > 50 first keeps only active students, then shows cities with more than 50 of them. Filtering in WHERE when possible is faster because fewer rows are grouped.
24

Open and close an accessible modal using the native dialog element.

DOM and Browser EventsMedium
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The dialog element handles focus and the Escape key for you: <button id='open'>Enquire now</button> <dialog id='enquiry'> <form method='dialog'> <p>Thank you for your interest.</p> <button>Close</button> </form> </dialog> <script> const dlg = document.getElementById('enquiry'); document.getElementById('open').addEventListener('click', () => dlg.showModal()); </script> showModal places it in the top layer with a backdrop, and form method='dialog' closes it without a request.
25

What is the difference between pseudo-classes and pseudo-elements?

CSS Layout and Responsive DesignEasy
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A pseudo-class selects an element in a particular state, such as :hover, :focus, :nth-child(2) or :checked, and uses a single colon. A pseudo-element styles a specific part of an element or inserts generated content, such as ::before, ::after, ::first-line or ::placeholder, and uses a double colon. For example, a::after can add an arrow icon after links without extra HTML.
26

You see 'Headers already sent' warnings. What causes it and how do you fix it?

PHP ProgrammingEasy
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header(), setcookie() and session_start() must run before any output reaches the browser. The warning appears when something was printed earlier, such as an echo, HTML outside PHP tags, whitespace after a closing ?> tag, or a UTF-8 BOM at the start of a file. The message names the file and line that produced output. Removing closing ?> tags in pure PHP files prevents most cases.
27

Your frontend on one domain gets a CORS error calling your API on another. How do you resolve it?

Web SecurityMedium
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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 would you explain a technical problem to a non-technical client?

DOM and Browser EventsEasy
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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.
29

How do srcset and sizes help with responsive images?

HTML FundamentalsMedium
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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.
30

What is the difference between Promises and async/await?

JavaScript CoreMedium
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A Promise represents a value that will be available later, handled with then and catch chains. async/await is syntax built on promises: an async function always returns a promise, and await pauses that function until the promise settles, making code read top to bottom. Errors are handled with try and catch. For parallel work you still use Promise.all, because awaiting calls one by one runs them sequentially.

Frequently asked questions

What happens in the Web Development telephonic interview round?

The telephonic or screening round is a 15-30 minute call with a recruiter or engineer. It checks your basics, your CV and whether you can explain Web Development concepts clearly without a screen to point at.

How do I clear the telephonic interview round?

Keep your CV in front of you and be ready to explain every line on it. Answer in short, clear sentences; there is no whiteboard, so structure matters. Take the call somewhere quiet and confirm the time in advance.

Which round comes next?

A typical order is online assessment, telephonic screening, one or two technical rounds, a managerial round and HR. Use the other round pages to practise each stage.

Practise every interview round

Online Assessment questionsTechnical Round questionsManagerial Round questionsRapid-Fire questionsHR & behavioural questionsFull mock interview

More ways to practise

Company-wise Web Development questionsExperience-wise Web Development questionsRole-wise Web Development questionsCity-wise Web Development questionsMost asked Web Development questionsScenario-based questionsPractical / hands-on questionsHR & behavioural questionsWeb Development mock interviewOnline assessment questionsTechnical round questionsManagerial round questionsWeb Development topic sheets