How to retrieve the responseXML from the xmlhttprequest? [duplicate]

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• How to return the response from an Ajax call? 6 answers

Ok before you mark this as duplicate read my question please. I have some xml file on the server and I want to access it asynchronously, which I am able to do, the problem I am having is that I cant access the xml DOM returned by the xmlhttprequest. Here is my code.

function getXML(filename, callback) {
    httpRequest = new XMLHttpRequest();
    httpRequest.onreadystatechange = function () {
    if (httpRequest.readyState === 4) { // request is done
        if (httpRequest.status === 200) { // successfully
            callback(httpRequest.responseXML); // we're calling callback method
        }
    }
    };
    httpRequest.open('GET', filename, true);
    httpRequest.send(null);
}

Here I call the loadXML with a callback function and a filename as an argument.

getXML("testfile.xml", function (result) { 
    xmldoc = result;
    console.log(subjectsDoc);  //This works fine. I get the xml file.
}); 

Then I want to be able to access the XML document. But I get an error.

subjects = xmlDoc.getElementsByTagName("test"); //Error: "xmldoc is undefined"