Exempt one xml attribute to be converted into a string when JSON result is returned

Question

I am using xml2js module of npm. It converts my xml to JSON. Suppose my xml is

<root>
    <fname>Akhil</fname>
    <lname>Sahni</lname>
    <timestamp>ISODate("2016-08-31T13:18:57.050Z")</timestamp>
</root>

so it returns me a JSON object as

{
  "fname":"Akhil",
  "lname":"Sahni",
  "timestamp" : "ISODate("2016-07-21T13:20:59.311Z")"
}

Note that the time stamp is a literal string with open/close quote problems. I want my JSON to be

{
  "fname":"Akhil",
  "lname":"Sahni",
  "timestamp" : ISODate("2016-07-21T13:20:59.311Z")
} 

ISODate is now a descriptor.