JavaScript AJAX Callback Functions as Parameter

Question

I would like to pass as parameter a generic function to be the onreadystate function , how can i do that and acess the xmlhttpobj ? Something like that:

    function xmlHttp(target, xml, readyfunc) {
        if (window.XMLHttpRequest) {
            httpObj = new XMLHttpRequest();
        } else if (window.ActiveXObject) {
            httpObj = new ActiveXObject("Microsoft.XMLHTTP");
        }
        if (httpObj) {
            httpObj.onreadystatechange = readyfunc;
            httpObj.open("POST", target, true);
            httpObj.send(xml);
        }
    }
    function Run (Place){
       if (xmlhttp.readyState==4 && xmlhttp.status==200)
            //do a lot of things in "Place"
   }

Answer 1

The function will be called in the context of the XHR object that the readychange event fires on.

Use this inside the function to reference the object.

Answer 2

All you should do is using this keyword or changing your code like this:

function Run (){
   if (this.readyState==4 && this.status==200){
        //do a lot of things in "Place"
   }
}

the other way is passing the xhr object as an argument:

httpObj.onreadystatechange = function(){
    readyfun(this);
};

then you should change the Run function like:

function Run(httpObj){
   if (httpObj.readyState==4 && httpObj.status==200){
        //do a lot of things in "Place"
   }
}

now you could call the xmlHttp function like this:

xmlHttp(target, xml, Run);

or

xmlHttp(target, xml, function(httpObj){
    Run(httpObj);
});