JavaScript: AJAX GET request

var get = function(url, callback, error, format){
	if(!format) format = "json";
	var xmlhttp = window.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject("Microsoft.XMLHTTP");
	
	xmlhttp.onreadystatechange = function() {
		if(xmlhttp.readyState == 4){
			if(xmlhttp.status == 200){
				if(typeof callback === "function") callback(format == "json" ? JSON.parse(xmlhttp.responseText) : xmlhttp.responseText);
			} else {
				if(typeof error === "function") error(format == "json" ? JSON.parse(xmlhttp.responseText) : xmlhttp.responseText);
			}
		}
	}
	
	xmlhttp.open("GET", url, true);
	xmlhttp.send();
}

get("url", function success(data){ console.log(data) }, function error(data){ console.log(data) }, "json");