Fetches all css stylesheets and extracts all image urls. Comes in handy when you want to preload your css asstets. See implementation for usage instructions.

cssimagecollect.js

/**
 * ===================================================================================
 * @name CssImageCollect
 * @version 1
 * @description a javascript css-image preloader
 * @author Thomas Appel, mail(at)thomas-appel(dot)com
 *
 * released under the MIT licence
 * copyright © 2011 Thomas Appel, thomas-appel.com
 *
 * changelog:
 * ===================================================================================
 * - 
 * ===================================================================================
 *
 * options:
 * ===================================================================================
 * turbo : bool // well, as it says.
 * preload : bool // you can disable preloading and just return an image array
 *
 * examples:
 * ===================================================================================
 * see implementation.js 
 * ===================================================================================
 */


(function( global ){
	/*
		if ( !global.document.styleSheets  ) {
			return false;
		}
	*/
	if ( !Object.create ) {
		Object.prototype.create = function( o ) {
			var F = function(){};		
			F.prototype = o;
			return new F();
		};
	}
	
	var CssImageCollect = (function(){
		
		var that, sheets = []; 
		
		function objectExtend( o, ref ) {
			var i;
			for ( i in ref ) {
				// no additional methods and properties may be passed to the original Object
				if ( o.hasOwnProperty(i) && ref.hasOwnProperty(i) ) {
					o[i] = ref[i];	
				}				
			}			
		}
		
		/*
		 * NOTE ON $MSIE
		 * ===================================================================================
		 * MSIE messes up the DOM css href property output of imported stylesheets.
		 * it includes styles correctly though, but here we have to "create" the real path,
		 * assuming the parent stylesheet's path is correct as it was direclty pulled from the
		 * first level document.styleSheet-Object, and thus should be a valid path.
		 * ===================================================================================
		 */			
		function arrayObj ( input ) {
			var cssPath = input.owningElement && input.owningElement.href ?
							input.owningElement.href :
							input.href,
				this_url = cssPath ? cssPath.replace(/[^\/]+\.(css.*)/,'') : null,
				obj = {
					sheet:input,
					href:this_url
				};
			return obj;
		}
		
		function getSheets ( input, arr, i, arg ) {
			var self = this,
				this_rules,
				is_msie = input[0] ? input[0].rules : null,
				this_sheets,
				this_sheets_rules,
				this_import_rules;

			while ( i-- ) {
				this_rules = input[i].cssRules || input[i].rules;
				if (!!this_rules){
					!!input[i].href && arr.push( arrayObj( input[i] ) );
					this_import_rules = this_rules;
					getSheets.call( this,this_import_rules,arr, this._max( this_import_rules.length ) );
					this_sheets = null;
				}
				try {
					this_sheets = input[i].styleSheet || input[i].imports;
					if ( !!this_sheets ){
						this_sheets_rules = this_sheets.cssRules || this_sheets;
						// dont push if is MSIE
						!is_msie && arr.push( arrayObj( this_sheets ) );
						getSheets.call( this, this_sheets_rules, arr, this._max( this_sheets_rules.length ) );
					}
				}
				catch(e){
					window.console && console.warn(e);
				}
			}
			return arr;
		}
		
		function imPath( im, rules, i ){
			if (! !!im[0].match(/^(http|https|ftp|file|):\/\/.*?/)){ // external URL					   
				im = rules[i].href + im[0];
			}	else {			
				im = im[0];
			}				   
			return im;
		}
		function uniqueArray( ar ) {
			var sorter, out, len, i, j;
			if( ar.length && typeof ar!=='string') {
				sorter = {};out = [];				
				len = ar.length;
				j=len;
				for(i=0;i<j;i++) {
					if( !sorter[ar[i]+typeof ar[i]] ) {
						out.push(ar[i]);
						sorter[ar[i]+typeof ar[i]] = true;
					}
				}
			}
			return out || ar;
		}					
				
		that = Object.create( {
			
			indexSheets : function() {
				return getSheets.apply( this, [ global.document.styleSheets, sheets, global.document.styleSheets.length ] );
			},
			getSheets : function() {
				return sheets;	
			},
		
			getCssImageURLs : function( raw ) {			
				var im,cssText,											  
					i, j, regex = /[^\"\(\)]+\.(gif|jpg|jpeg|png|svg|bmp)/g,
					images=[],
					rules = sheets,
					style_rules;
			/*
			 * ===================================================================================
			 * actually we don't have to care about relative paths
			 * we just need the rel path, e.g. webkit, etc. prints out the complete path;
			 * so, if the complete path matches the out location, shorten it
			 * ===================================================================================
			 */
					i = rules.length;
					while (i--){
						style_rules = rules[i].sheet.cssRules ? rules[i].sheet.cssRules :rules[i].sheet.rules; //msie fallback, note: also safari can handle the 'rules' property
						j = style_rules.length;
						
						while (j--){
							cssText = style_rules[j].cssText ? style_rules[j].cssText :style_rules[j].style.cssText;
							if (cssText.match(/base64/)){continue;}
							
							im = cssText.match( regex );
	
							if (im) {							
								im = imPath( im, rules, i );
								images.push( im );
								im = null;
							}
						}
					}				
				return raw ? images : uniqueArray( images );
			},
			
			_max : function( len ){
				return this.settings.turbo ? Math.min( len , 20 ) : len;
			}
		});
		
		return function ( options ) {
			var self = that, arr = [],
				temp_src;
						
			that.settings = {
				turbo : false
			}
			// extend settings with user options
			objectExtend( that.settings, options );
			that.indexSheets();
			return that;
		}
	}());
	
	if ( !global.TA ) {
		global.TA = {};
		
	}
	if ( !global.TA.UTILS ) {
		global.TA.UTILS = {};
	}
	
	global.TA.UTILS.CssImageCollect = CssImageCollect;
 
}( this ));

implementation.js

        /**
        * CssImageCollect can be called with an optional configuration literal
        * which takes one property called 'turbo' 
        * Set 'turbo' to true, if you want CssImageCollect to search 
        * only the first 20 rules of each stylesheet for @import rules
        */

	var cssAssets = TA.UTILS.CssImageCollect({
		turbo:true
	});

        /**
        * returns all image paths found in stylesheets as an javascript array
        * set argument to true, if you don't want to return a unified array
        */
        cssAssets.getCssImageURLs( true ); 

        /**
        * returns all css stylesheet objects in an javascript array
        */
        cssAssets.getSheets( );

        /**
        * re-indexes all stylesheets
        */
        cssAssets.indexSheets( );