How Wikipedia implements srcset in js

wikipedia-srcset.js

  	$.fn.hidpi=function(){
			var $target=this,devicePixelRatio=$.devicePixelRatio(),testImage=new Image();
			if(devicePixelRatio>1&&testImage.srcset===undefined){
				$target.find('img').each(function(){
					var $img=$(this),srcset=$img.attr('srcset'),match;
					if(typeof srcset==='string'&&srcset!==''){
						match=$.matchSrcSet(devicePixelRatio,srcset);
						if(match!==null){
							$img.attr('src',match);
						}
					}
				}
				);
			}
			return $target;
		}
		;
		$.matchSrcSet=function(devicePixelRatio,srcset){
			var candidates,candidate,bits,src,i,ratioStr,ratio,selectedRatio=1,selectedSrc=null;
			candidates=srcset.split(/ *, */);
			for(i=0;
			i<candidates.length;
			i++){
				candidate=candidates[i];
				bits=candidate.split(/ +/);
				src=bits[0];
				if(bits.length>1&&bits[1].charAt(bits[1].length-1)==='x'){
					ratioStr=bits[1].substr(0,bits[1].length
-1);
					ratio=parseFloat(ratioStr);
					if(ratio<=devicePixelRatio&&ratio>selectedRatio){
						selectedRatio=ratio;
						selectedSrc=src;
					}
				}
			}
			return selectedSrc;
		}
		;
	}