JSONP simple implementation

jsonp.js

(function(global,document){
	var uid = 0 ;
	
	function getJSON(url,callback){
		var elem;

		uid ++;
		getJSON.callbacks[uid] = callback;

		url = filterUrlCallback(url);
		if(url.indexOf('?') !== -1){
			url = url + '&callback=getJSON.CALLBACK';
		}else{
			url = url + '?callback=getJSON.CALLBACK'
		}

		elem = createScript();
		addEventListener(elem);
		elem.src = url;
		document.head.appendChild(elem);
	}

	function filterUrlCallback(url){
		var cbRegex = /((\??)callback=\w*(&?))/;
		if(typeof url === 'string' ){
			url = url.replace(cbRegex,function(all,match,prefix,post){
				return prefix && post ? prefix : '';
			})
		}
		return url
	}

	function createScript(){
		var elem = document.createElement('script');
		elem.type = 'text/javascript';
		elem.id = uid + '_id';

		return elem
	}

	function addEventListener(elem){
		if (!isElement(elem)){ return }
		elem.addEventListener('load',function(){
			var id = parseInt(elem.id),
				callback = getJSON.callbacks[id],
				response = getJSON.response[id];

			callback.call(null,response);
			cleanHook(elem);
		})
	}

	function cleanHook(elem){
		var id = parseInt(elem.id);

		getJSON.callbacks[id] = undefined;
		getJSON.response[id] = undefined;

		document.head.removeChild(elem);
	}

	function isElement(o){
		return o && typeof o === 'object' && o !== null && o.nodeType === 1 && typeof o.nodeName === 'string' 
	}

	getJSON.callbacks = {};
	getJSON.response = {};

	getJSON.CALLBACK = function(response){
		return getJSON.response[uid] = response
	}

	global.getJSON = getJSON;

})(window,document)