スクリプト：retina.js

retina.js

// retina.js, a high-resolution image swapper (http://retinajs.com), v0.0.2

(function(){function t(e){this.path=e;var t=this.path.split("."),n=t.slice(0,t.length-1).join("."),r=t[t.length-1];this.at_2x_path=n+"@2x."+r}function n(e){this.el=e,this.path=new t(this.el.getAttribute("src"));var n=this;this.path.check_2x_variant(function(e){e&&n.swap()})}var e=typeof exports=="undefined"?window:exports;e.RetinaImagePath=t,t.confirmed_paths=[],t.prototype.is_external=function(){return!!this.path.match(/^https?\:/i)&&!this.path.match("//"+document.domain)},t.prototype.check_2x_variant=function(e){var n,r=this;if(this.is_external())return e(!1);if(this.at_2x_path in t.confirmed_paths)return e(!0);n=new XMLHttpRequest,n.open("HEAD",this.at_2x_path),n.onreadystatechange=function(){return n.readyState!=4?e(!1):n.status>=200&&n.status<=399?(t.confirmed_paths.push(r.at_2x_path),e(!0)):e(!1)},n.send()},e.RetinaImage=n,n.prototype.swap=function(e){function n(){t.el.complete?(t.el.setAttribute("width",t.el.offsetWidth),t.el.setAttribute("height",t.el.offsetHeight),t.el.setAttribute("src",e)):setTimeout(n,5)}typeof e=="undefined"&&(e=this.path.at_2x_path);var t=this;n()},e.devicePixelRatio>1&&(window.onload=function(){var e=document.getElementsByTagName("img"),t=[],r,i;for(r=0;r<e.length;r++)i=e[r],t.push(new n(i))})})();