XML DOM replaceData() Method

var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
    if (xhttp.readyState == 4 && xhttp.status == 200) {
        myFunction(xhttp);
    }
};
xhttp.open("GET", "books_cdata.xml", true);
xhttp.send();

function myFunction(xml) {
    var xmlDoc = xml.responseXML;
    var x = xmlDoc.getElementsByTagName("html")[0].childNodes[0];
    x.replaceData(3, 8, "Fantastic");
    document.getElementById("demo").innerHTML =
    x.data;
}

CDATANode.replaceData(start,length,string)