How to print xml string from xmlDoc

I am doing is reading xml document from server and i have to make modification to that xml document locally and store the xml document response on server but i am not able to print the changed xml response please help me!!!!

function loadXMLDoc(dname)
{
if (window.XMLHttpRequest)
{
    xhttp=new XMLHttpRequest();
}
else
{
    xhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
xhttp.open("GET",dname,false);
xhttp.send();
return xhttp.responseXML;
}


function stringsxmlparsing()
{
console.log("\n\nThis is books.xml demo\n\n");

xmlDoc=loadXMLDoc("books.xml");

//Changing attribute value
x=xmlDoc.getElementsByTagName('string');
x[0].setAttribute("name","food");

//Accessing attribute value
txt=xmlDoc.getElementsByTagName("string")[0].getAttribute("name");
console.log("getAttribute value :"+txt

 //here i have to send response xml to server

 //I have tried  
 //console.log(xmlDoc.toXMLString()) but won't worked
}