What is the purpose of the 'use strict' directive in JavaScript?
The 'use strict' directive enforces a stricter set of parsing and error handling rules in JavaScript. It helps catch common coding errors and prevents the use of certain error-prone features.
Example:
```javascript 'use strict'; // Strict mode code goes here ```
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Responsive web design is an approach that makes web pages render well on a variety of devices and window or screen sizes. It uses flexible grids and layouts, along with media queries.
Example:
```css @media only screen and (max-width: 600px) { body { font-size: 14px; } }```
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What is the purpose of the 'defer' attribute in a script tag?
The 'defer' attribute in a script tag tells the browser to execute the script after the HTML is completely parsed, but before firing the DOMContentLoaded event.
Example:
```html ```
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What is the purpose of the 'localStorage' and 'sessionStorage' objects in JavaScript?
'localStorage' and 'sessionStorage' are Web Storage APIs for storing key-value pairs in a web browser. 'localStorage' persists data even after the browser is closed, while 'sessionStorage' stores data for the duration of a page session.
Example:
```javascript // Storing data in localStorage localStorage.setItem('username', 'JohnDoe');
// Retrieving data from localStorage const username = localStorage.getItem('username'); ```
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What is the difference between 'inline' and 'block' elements in CSS?
'inline' elements only take up as much width as necessary and do not start on a new line. 'block' elements take up the full width available and start on a new line.
Example:
```css /* Inline element example */ span { display: inline; }
/* Block element example */ div { display: block; }```
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What is the purpose of the 'data-' attribute in HTML?
The 'data-' attribute is used to store custom data private to the page or application. It provides a way to attach additional information to HTML elements without using non-standard attributes.
Example:
```html This is a custom element.
```
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Explain the purpose of the 'rem' unit in CSS and how it differs from 'em'.
'rem' (root em) is relative to the font-size of the root element, while 'em' is relative to the font-size of the nearest parent element with a font-size. 'rem' is not affected by the parent element's font-size.
Example:
```css html { font-size: 16px; }
body { font-size: 1.5rem; /* 24px */ } ```
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Explain the difference between 'cookie', 'sessionStorage', and 'localStorage'.
'cookie' is a small piece of data stored on the client's computer, 'sessionStorage' stores data for the duration of a page session, and 'localStorage' persists data even after the browser is closed.
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Explain the concept of 'event bubbling' in JavaScript.
'Event bubbling' is the process where the event starts from the target element and bubbles up the DOM hierarchy until it reaches the root. It allows for delegating event handling to a common ancestor.
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What is the purpose of the 'transition' property in CSS?
The 'transition' property in CSS is used to create smooth transitions between property values over a specified duration. It is commonly used for animations and effects.
Example:
```css /* Example of using transition */ .element { transition: width 0.5s ease-in-out; } ```
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What is the role of the 'viewport' meta tag in HTML?
The 'viewport' meta tag in HTML is used to control the layout viewport of the browser, ensuring that the webpage is displayed correctly on various devices by setting the initial scale, width, and zoom level.
Example:
```html ```
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