utm_tracking

(function($) {
	$.fn.utm_tracking = function(domain, source, medium, campaign) {
		$(this).find('a[href^="' + domain + '"]').each(function() {
			var url = $(this).attr('href');
			$(this).attr( 'href', url + '?utm_source=' + source + '&utm_medium=' + medium + '&utm_campaign=' + campaign );
		});
	}
	$.fn.utm_tracking_via_obj = function(domain, utmObj) {
		utmObj = utmObj || $.utm_data_from_url();
		$(this).find('a[href^="' + domain + '"]').each(function() {
			var url = $(this).attr('href');
			$(this).attr( 'href', $.utm_data_replace_in_url(utmObj,url) );
		});
	}
	$.utm_data_from_url = function(inUrl) {
	  var outObject = {}, urlChange = inUrl || (window.location.href);
	  urlChange = ((urlChange.charAt(0) === '?' && urlChange.substring(1)) || urlChange.split('?').slice(1).join('?') );
	  if (urlChange.length <= 0)
	  	return null;
	  $.each(urlChange.split('&'), function(i,v){ if ($.inArray(v.split('=')[0],['utm_campaign','utm_medium','utm_source']) !== -1) outObject[v.split('=')[0]] = v.split('=')[1]; });
	  outObject.toString = function() {
	  	var outString = [];
	  	$.each(outObject, function(i,v) { typeof v !== 'function' && outString.push(i+'='+v); })
	  	return outString.join('&');
	  }
	  return outObject;
	}
	$.utm_obj_to_suffix = function(utmObj, inUrl) {
	  var outUrl = inUrl || window.location.href;
	  return outUrl.indexOf('?') !== -1 ? outUrl + '&' + utmObj.toString() : outUrl + '?' + utmObj.toString();
	}
	$.utm_data_replace_in_url = function(newUtm, inUrl) {
	  var outUrl = inUrl || window.location.href, 
	  	  oldUtms = $.utm_data_from_url(inUrl);
	  if (oldUtms) {
		  $.each(oldUtms, function(i,v){ 
		  	if (typeof v !== 'function')
		  		outUrl = outUrl.replace(i + '=' + v,'');
		  });
		  outUrl = outUrl.replace(/&$/,'').replace('&&','&').replace('&&','&').replace('?&','?').replace(/&$/,'').replace(/\?$/,'');
	  } 
	  return $.utm_obj_to_suffix(newUtm, outUrl);
	}
}(jQuery));

//Examples

$(document).ready( function() {
     $('body').utm_tracking('http://www.example.com','example_source','example_link','example_campaign'); //Thanks, Devin
     
     $('body').utm_tracking_via_obj('http://www.example.com'); // Uses UTM data from current URL, replaces them in object attributes
     $('body').utm_tracking_via_obj('http://www.example.com', $.utm_data_from_url('?utm_campaign=foobar') ); // Uses UTM data from the second parameter's querystring (IE: utm_campaign=foobar in this case)
     
});