Browser or Native browser environment detection I use this script/class to help me write those nasty forks in my JS for different browsers, OSs, plateform(mobile, desktop), and of course pixel density. This is proudly based on http://www.quirksmode.org/js/detect.html

Javascript Environment Detection

window.Example = window.Example || {};

Example.Environment = function() {
  var
			_$win = $( window );

	var environment = {
			init: function () {

				this.browser = this._searchString( this.dataBrowser ) || "An unknown browser";
				this.version = this._searchVersion( navigator.userAgent )
					|| this._searchVersion( navigator.appVersion )
					|| "an unknown version"
				;

				//this.platform = this.searchPlatform();
				this.OS = this._searchString( this.dataOS ) || "an unknown OS";

				// is mobile (ipad, iphone, android)
				this.isMobile = this._determineMobile( this.dataMobileBrowsers );

				// currently we assume only mobile devices are touch
				this.isTouch = this.isMobile;

				// is native
				this.isNative = this._determineNative();

				// viewport
				this.viewport = this.calculateViewport();

				this.resolution = this._determineResolution();

				this.isHighResolution = this._determineHighResolution();

				// console.log('browser: ' + this.browser);
				// console.log('version: ' + this.version);
				// console.log('OS: ' + this.OS);
				// console.log('isMobile: ' + this.isMobile);
				// console.log('isNative: ' + this.isNative);
				// console.log('isHighResolution: ' + this.isHighResolution);
				// console.log(this.viewport.width + "x" + this.viewport.height);
				// console.log(this.resolution.width + "x" + this.resolution.height);
			}


			/**
			 * Searches an array of data looking for specific values
			 * Used to determine the browser and the OS.
			 *
			 * @param  {Array} data Array of strings to look through
			 * @return {String} The parsed string that was found (browser or OS)
			 */
		,	_searchString: function ( data ) {
				var
					i = 0
				,	len = data.length
				;
				for ( i=0;i<len;i++ )	{
					var dataString = data[ i ].string;
					var dataProp = data[ i ].prop;
					this.version_searchString = data[ i ].versionSearch || data[ i ].identity;
					if (dataString) {
						if (dataString.indexOf(data[i].subString) !== -1) {
							return data[ i ].identity;
						}
					}
					else if (dataProp) {
						return data[ i ].identity;
					}
				}
			}

			/**
			 * Method determines the browser version.
			 *
			 * @param  {String} dataString String to parse to look for the verion number
			 * @return {String}            Version Number
			 */
		,	_searchVersion: function (dataString) {
				var index = dataString.indexOf( this.version_searchString );
				if (index === -1) {
					return;
				}

				return parseFloat( dataString.substring( index + this.version_searchString.length + 1 ) );
			}

			/**
			 * Method determines if the platform is mobile (based on OS)
			 * @param  {[type]} data [description]
			 * @return {[type]}      [description]
			 */
		,	_determineMobile: function( data ) {
				var
					i = 0
				,	len = data.length
				;
				for ( i = 0; i < len; i++ )	{
					var identity = data[ i ].identity;

					console.log('identity; ' + identity);

					if (this.OS.indexOf( identity ) !== -1) {
						return true;
					}
				}

				return false;
			}

			/**
			 * Method determines if the app is running as a native application
			 */
		,	_determineNative: function() {
				//console.log("window.device: " + window.device);
				return ( window.device !== undefined );
			}
			/**
			 * Method determines the systems screen resolution
			 * @return {Object} Object contain the screen's width and height
			 */
		,	_determineResolution: function() {
				return {
					width: screen.width
				,	height: screen.height
				};
			}

		,	_determineHighResolution: function() {
				var pixelRatio = window.devicePixelRatio ? window.devicePixelRatio : 1;

				if(pixelRatio >= 2) {
					return true;
				}
				else {
					return false;
				}
			}
			/**
			 * Method calculates the viewport size of the current browser.
			 * @return {Object} Object contains the screen's width and height
			 */
		,	calculateViewport: function() {
				this.viewport =  {
					width: _$win.width()
				,	height: _$win.height()
				};

				console.log(this.viewport.width + "x" + this.viewport.height);

				return this.viewport;
			}

		,	dataBrowser: [
				{
					string: navigator.userAgent,
					subString: "Chrome",
					identity: "Chrome"
				}
			,	{	string: navigator.userAgent,
					subString: "OmniWeb",
					versionSearch: "OmniWeb/",
					identity: "OmniWeb"
				}
			,	{
					string: navigator.vendor,
					subString: "Apple",
					identity: "Safari",
					versionSearch: "Version"
				}
			,	{
					prop: window.opera,
					identity: "Opera",
					versionSearch: "Version"
				}
			,	{
					string: navigator.vendor,
					subString: "iCab",
					identity: "iCab"
				}
			,	{
					string: navigator.vendor,
					subString: "KDE",
					identity: "Konqueror"
				}
			,	{
					string: navigator.userAgent,
					subString: "Firefox",
					identity: "Firefox"
				}
			,	{
					string: navigator.vendor,
					subString: "Camino",
					identity: "Camino"
				}
			,	{		// for newer Netscapes (6+)
					string: navigator.userAgent,
					subString: "Netscape",
					identity: "Netscape"
				}
			,	{
					string: navigator.userAgent,
					subString: "MSIE",
					identity: "Explorer",
					versionSearch: "MSIE"
				}
			,	{		// for older Netscapes (4-)
					string: navigator.vendor,
					subString: "Google",
					identity: "Android",
					versionSearch: "Version"
				}
			,	{
					string: navigator.userAgent,
					subString: "Gecko",
					identity: "Mozilla",
					versionSearch: "rv"
				}
			,	{		// for older Netscapes (4-)
					string: navigator.userAgent,
					subString: "Mozilla",
					identity: "Netscape",
					versionSearch: "Mozilla"
				}
			]
		,	dataMobileBrowsers : [
				{
					identity: "iPad"
				}
			,	{
					identity: "iPhone"
				}
			,	{
					identity: "Android"
				}
		]

		,	dataOS : [
				{
					string: navigator.platform,
					subString: "Win",
					identity: "Windows"
				}
			,	{
					string: navigator.userAgent,
					subString: "Android",
					identity: "Android"
				}
			,	{
					string: navigator.platform,
					subString: "Mac",
					identity: "Mac"
				}
			,	{
					   string: navigator.userAgent,
					   subString: "iPhone",
					   identity: "iPhone/iPod"
			    }
			,	{
					   string: navigator.userAgent,
					   subString: "iPad",
					   identity: "iPad"
			    }
			,	{
					string: navigator.platform,
					subString: "Linux",
					identity: "Linux"
				}
			]
	};

	environment.init();
	return environment;
};