sizes-detection.js

(function(){
	'use strict';
	var width2 = 'data:image/gif;base64,R0lGODlhAgABAPAAAP///wAAACH5BAAAAAAALAAAAAACAAEAAAICBAoAOw==';
	var width1 = 'data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==';
	var img = document.createElement('img');
	var test = function(){
		var width = img.width;

		if(width == 2){
			alert('your browser support sizes');
		} else {
			alert('your browser does not support sizes');
		}
	};

	img.onload = test;
	img.onerror = test;
	img.setAttribute('sizes', '9px');

	img.srcset = width1 + ' 1w,' + width2 + ' 8w';
	img.src = width1;
})();