Find breakPoints by searching through the document.styleSheets

breakPoints

/*global signals, CSSMediaRule*/
window.breakPoints = (function(signal){
	'use strict';
	window.addEventListener('load',function(){
		var forEach = Array.prototype.forEach
			,aSizes = [Number.MAX_VALUE]
			,iSizes
			,iCurrent = -1
		;
		// loop styleSheets, then cssRules, then media
		forEach.apply(document.styleSheets,[function(styleSheet){
			if (styleSheet.href!==null) {
				forEach.apply(styleSheet.cssRules,[function(rule){
					if (rule.constructor===CSSMediaRule) {
						if (rule.media.length>0&&rule.media[0]===undefined) { // see: http://msdn.microsoft.com/en-us/library/ff460307(v=vs.85).aspx
							findBreakpoint(rule.media.mediaText);
						} else {
							forEach.apply(rule.media,[function(medium){
								findBreakpoint(medium);
							}]);
						}
					}
				}]);
			}
		}]);
		aSizes.sort(function(a,b){return a>b?1:-1;});
		iSizes = aSizes.length;
		signal.current = iCurrent;
		signal.points = aSizes;
		if (iSizes!==0) {
			window.addEventListener('resize',handleResize);
			handleResize();
		} else {
			console.warn('No breakpoints found');
		}

		/**
		 * Searches string for breakpoint to add to the list.
		 * @param medium {string}
		 */
		function findBreakpoint(medium){
			var aMatch = medium.match(/\(([^\)]+)\)/g);
			aMatch&&aMatch.forEach(function(match){
				var aWidth = match.match(/width/)
					,aDigit = match.match(/\d+/)
					,bMax = !!match.match(/max/)
				;
				if (aWidth&&aDigit) {
					var iSize = parseInt(aDigit.pop()) + (bMax?1:0);
					if (aSizes.indexOf(iSize)===-1) aSizes.push(iSize);
				}
			});
		}

		/**
		 * Handle resize event to check which breakpoint we are at.
		 * Dispatches signal when breakpoint changes
		 */
		function handleResize(){
			var iWindowWidth = window.innerWidth;
			var iCheckSize = aSizes[0];
			for (var i=0;i<iSizes;i++) {
				iCheckSize = aSizes[i];
				if (iWindowWidth<iCheckSize) {
					break;
				}
			}
			if (iCheckSize!==iCurrent) {
				var iOld = iCurrent;
				iCurrent = iCheckSize;
				signal.current = iCurrent;
				signal.dispatch(iCurrent,iOld);
			}
		}
	},false);
	return signal;
})(new signals.Signal());