https://github.com/abdmob/x2js - my own library (updated URL from http://code.google.com/p/x2js/):

This library provides XML to JSON (JavaScript Objects) and vice versa javascript conversion functions. The library is very small and doesn't require any other additional libraries.

API functions

• new X2JS() - to create your instance to access all library functionality. Also you could specify optional configuration options here
• X2JS.xml2json - Convert XML specified as DOM Object to JSON
• X2JS.json2xml - Convert JSON to XML DOM Object
• X2JS.xml_str2json - Convert XML specified as string to JSON
• X2JS.json2xml_str - Convert JSON to XML string

Online Demo on http://jsfiddle.net/abdmob/gkxucxrj/1/

var x2js = new X2JS();
function convertXml2JSon() {
    $("#jsonArea").val(JSON.stringify(x2js.xml_str2json($("#xmlArea").val())));
}

function convertJSon2XML() {
    $("#xmlArea").val(x2js.json2xml_str($.parseJSON($("#jsonArea").val())));
}

convertXml2JSon();
convertJSon2XML();
$("#convertToJsonBtn").click(convertXml2JSon);
$("#convertToXmlBtn").click(convertJSon2XML);