fbtracker.js

if (window.location.search != '') {
	var fb_campaign_id = '';
	var search_items = window.location.search;
	search_items = search_items.replace('?', '');

	search_items = search_items.split('&&');
	for(i=0;i<search_items.length;i++){
	    var thisItem = search_items[i];
	    if(thisItem.indexOf('utm_medium') > -1){
	        var getCampaign = thisItem.split("=");
	        fb_campaign_id = getCampaign[1];

	        var buyLinkList = document.getElementsByClassName('buyBtn');
			for(i=0;i<buyLinkList.length;i++){
			    var newURL = buyLinkList[i].href+'?attributes[fb_campaign_id]='+fb_campaign_id;
			    buyLinkList[i].href=newURL;
			}

	    }
	}
}