Most Asked Web Development Interview Questions with Detailed Answers

Example Answer:

“HTML is the standard markup language for web pages, with flexible syntax that browsers can interpret even with minor errors. XHTML, however, follows XML rules, requiring strict adherence to syntax, like closing all tags and using lowercase. For example, in HTML, <br> is valid, but in XHTML, it must be <br />. XHTML is useful for applications needing XML compatibility, but HTML is more common due to its flexibility.”

Explain the CSS Box Model.

The CSS Box Model describes how elements are rendered as rectangular boxes on a web page, consisting of:

• Content Box: The innermost layer with the element’s content (text, images, etc.).
• Padding: Transparent space around the content, styled with background properties.
• Border: Surrounds the padding and content, customizable with width, style, and color.
• Margin: Transparent space outside the border, separating the element from others.

The total width/height of an element is calculated as:

• Total Width = Content Width + Left Padding + Right Padding + Left Border + Right Border
• Total Height = Content Height + Top Padding + Bottom Padding + Top Border + Bottom Border

Example Answer:
“The CSS Box Model is how browsers render elements as boxes. For instance, if a div has a width of 100px, 10px padding on each side, and a 2px border, its total width is 124px (100 + 10 + 10 + 2 + 2). Understanding this helps in designing precise layouts, as margins and padding affect spacing and positioning.”

What are CSS Selectors?

CSS Selectors target HTML elements for styling. Common types include:

• Element Selector: Targets all elements of a type (e.g., p for paragraphs).
• ID Selector: Targets an element by its ID (e.g., #main).
• Class Selector: Targets elements by class (e.g., .intro).
• Universal Selector: Targets all elements (*).
• Attribute Selector: Targets elements by attributes (e.g., [href]).
• Pseudo-class Selector: Targets elements in a specific state (e.g., :hover).
• Pseudo-element Selector: Styles parts of an element (e.g., ::first-line).
• Combinators: Combine selectors (e.g., div p for <p> inside <div>).

Example Answer:
“CSS Selectors let you style specific HTML elements. For example, .button:hover changes a button’s style when hovered, and ul > li targets only direct <li> children of <ul>. Selectors are essential for precise styling and responsive design.”

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JavaScript

What is the difference between undefined and null in JavaScript?

In JavaScript, undefined and null both indicate no value but differ in usage:

• undefined: A variable declared but not assigned a value, or a function with no return value. It’s a global property (window.undefined in browsers).
• null: An intentional absence of value, assigned to indicate a variable is empty or has no object reference.

Key Differences:

• Type: typeof undefined is “undefined”; typeof null is “object” (a historical quirk).
• Assignment: undefined is automatic; null is explicitly set.
• Intent: undefined suggests a variable hasn’t been initialized; null indicates deliberate emptiness.

Example Answer:
“In JavaScript, undefined means a variable exists but hasn’t been assigned, like let x;. null is used to explicitly set a variable to no value, like let y = null. For example, checking if (x == null) catches both, but null is often used to clear object references.”

Explain closures in JavaScript.

A closure is a function that retains access to its outer function’s scope, even after the outer function has returned. This allows the inner function to use and modify variables from the outer scope.

Example: