Extremely simple AJAX call

simpleajax.js

function SimpleAJAX(url, body, callback){

    if(!callback && typeof body=="function"){
        callback = body;
        body = undefined;
    }

    var http = new XMLHttpRequest() || new ActiveXObject("Microsoft.XMLHTTP");
    
    http.open(body?'post':'get', url);
    http.onreadystatechange = function(){
        if(http.readyState == 4){
            if(http.status == 200){
                callback(null, http);
            }else{
                callback(new Error("Invalid response"));
            }
        }
    };
    body?http.send(body):http.send();
}

// Usage
SimpleAJAX("/post", "post body", function(error, response){
    if(error){
        alert("Error");
    }else{
        alert(response.responseText);
    }
});