jquery.retina.js

/*
	Author: Troy Mcilvena (http://troymcilvena.com)
	Twitter: @mcilvena
	Date: 24 November 2011
	Version: 1.3
	
	Revision History:
		1.0 (23/08/2010)	- Initial release.
		1.1 (27/08/2010)	- Made plugin chainable
		1.2 (10/11/2010)	- Fixed broken retina_part setting. Wrapped in self executing function (closure)
		1.3 (29/10/2011)	- Checked if source has already been updated (via mattbilson)
*/

(function( $ ){
	$.fn.retina = function(retina_part) {
		// Set default retina file part to '-2x'
		// Eg. some_image.jpg will become some_image-2x.jpg
		var settings = {'retina_part': '-2x'};
		if(retina_part) jQuery.extend(settings, { 'retina_part': retina_part });

		if(window.devicePixelRatio >= 2) {
			this.each(function(index, element) {
				if(!$(element).attr('src')) return;
				
				var checkForRetina = new RegExp("(.+)("+settings['retina_part']+"\\.\\w{3,4})");
				if(checkForRetina.test($(element).attr('src'))) return;

				var new_image_src = $(element).attr('src').replace(/(.+)(\.\w{3,4})$/, "$1"+ settings['retina_part'] +"$2");
				$.ajax({url: new_image_src, type: "HEAD", success: function() {
					$(element).attr('src', new_image_src);
				}});
			});
		}
		return this;
	}
})( jQuery );