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# System Information
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Extract detailed information about operating systems, browsers, and User-Agent characteristics from device strings.
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## Capabilities
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### User Agent Detection
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Identifies the primary browser or application from the User-Agent string.
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```javascript { .api }
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/**
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 * Returns the (first) detected user-agent string or null
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 * @returns The primary detected browser/application name or null
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 */
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userAgent(): string | null;
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```
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**Detected User Agents:**
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- **Browsers**: Chrome, Firefox, Safari, Edge, Opera, IE
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- **Mobile Browsers**: Opera Mini, Opera Mobi, UCBrowser, MQQBrowser, SamsungBrowser
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- **Applications**: MicroMessenger (WeChat), baiduboxapp, baidubrowser
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- **Engines**: Webkit, Gecko, Trident, Presto
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- **Other**: Coast, Dolfin, Fennec, NetFront, NokiaBrowser, Skyfire, Tizen
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**Usage Examples:**
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```javascript
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const MobileDetect = require('mobile-detect');
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// Chrome detection
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const chromeMd = new MobileDetect('Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36');
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console.log(chromeMd.userAgent()); // 'Chrome'
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// Safari on iPhone
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const safariMd = new MobileDetect('Mozilla/5.0 (iPhone; CPU iPhone OS 14_6 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/14.1.1 Mobile/15E148 Safari/604.1');
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console.log(safariMd.userAgent()); // 'Safari'
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// Firefox
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const firefoxMd = new MobileDetect('Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:89.0) Gecko/20100101 Firefox/89.0');
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console.log(firefoxMd.userAgent()); // 'Firefox'
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```
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### Multiple User Agents Detection
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Returns all detected user-agent identifiers from the User-Agent string.
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```javascript { .api }
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/**
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 * Returns all detected user-agent strings
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 * @returns Array of all detected browser/application names
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 */
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userAgents(): string[];
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```
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**Usage Examples:**
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```javascript
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// Complex User-Agent with multiple identifiers
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const complexMd = new MobileDetect('Mozilla/5.0 (Linux; Android 11; SM-G991B) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.120 Mobile Safari/537.36');
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console.log(complexMd.userAgent());  // 'Chrome' (first detected)
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console.log(complexMd.userAgents()); // ['Chrome', 'Safari', 'Webkit'] (all detected)
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// Simple case
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const simpleMd = new MobileDetect('Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:89.0) Gecko/20100101 Firefox/89.0');
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console.log(simpleMd.userAgents()); // ['Firefox', 'Gecko']
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```
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### Operating System Detection
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Identifies the operating system from the User-Agent string.
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```javascript { .api }
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/**
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 * Returns the detected operating system string or null
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 * @returns The operating system name or null if not detected
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 */
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os(): string | null;
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```
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**Detected Operating Systems:**
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- **Mobile**: iOS, AndroidOS, BlackBerryOS, webOS, Sailfish
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- **Desktop**: Windows NT, Mac OS X, Linux
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- **Other**: Symbian, Windows Phone OS, Windows Phone, Windows CE, BREW, Java
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**Usage Examples:**
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```javascript
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// iOS detection
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const iosMd = new MobileDetect('Mozilla/5.0 (iPhone; CPU iPhone OS 14_6 like Mac OS X)');
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console.log(iosMd.os()); // 'iOS'
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// Android detection  
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const androidMd = new MobileDetect('Mozilla/5.0 (Linux; Android 11; SM-G991B)');
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console.log(androidMd.os()); // 'AndroidOS'
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// Windows detection
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const windowsMd = new MobileDetect('Mozilla/5.0 (Windows NT 10.0; Win64; x64)');
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console.log(windowsMd.os()); // 'Windows NT'
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// macOS detection
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const macMd = new MobileDetect('Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7)');
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console.log(macMd.os()); // 'Mac OS X'
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```
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## System Categories
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### Mobile Operating Systems
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- **iOS**: iPhone, iPad, iPod touch operating system
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- **AndroidOS**: Google Android in all variants
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- **BlackBerryOS**: BlackBerry devices
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- **webOS**: Palm/HP webOS, LG webOS
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- **Sailfish**: Sailfish OS
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- **Windows Phone**: Microsoft mobile OS variants
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- **Symbian**: Nokia Symbian OS
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### Desktop Operating Systems
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- **Windows NT**: All modern Windows versions (7, 8, 10, 11)
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- **Mac OS X**: macOS in all versions
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- **Linux**: Various Linux distributions
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### Browser Engines
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- **Webkit**: Safari, Chrome, many mobile browsers
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- **Gecko**: Firefox and Mozilla-based browsers  
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- **Trident**: Internet Explorer
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- **Presto**: Older Opera versions
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- **Blink**: Chrome, newer Opera (detected as Webkit)
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## Implementation Notes
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- **Pattern Matching**: Uses regex patterns to identify system components
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- **Caching**: Results are cached per instance for performance
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- **Priority**: Returns first match for userAgent(), all matches for userAgents()
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- **Case Insensitive**: Detection is case-insensitive
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- **Version Support**: Use version() and versionStr() methods for version information
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- **Fallback**: Returns null when no pattern matches
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## Common Use Cases
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```javascript
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const md = new MobileDetect(navigator.userAgent);
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// Feature detection based on OS
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if (md.os() === 'iOS') {
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  // iOS-specific functionality
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} else if (md.os() === 'AndroidOS') {
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  // Android-specific functionality
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}
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// Browser-specific optimizations
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if (md.userAgent() === 'Safari') {
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  // Safari-specific code
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} else if (md.userAgent() === 'Chrome') {
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  // Chrome-specific code
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}
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// Multiple browser support check
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const agents = md.userAgents();
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if (agents.includes('Webkit')) {
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  // Webkit-based browser functionality
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}
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```