Check Dates using javascript

How can I check the value of a field that is defined as a date field after the date has been selected using javascript. I want to check the date chosen, and if it's not equal to a prededined date, alert the user. Below is the javascript that I threw together that gets me half way there.

function TEXT_OnBlur(id, row)
{
if (id != "text85") return true;
{
var vDmeString = portalWnd.DMEPath;
vDmeString += "?PROD="+strPDL;
vDmeString += "&FILE=APVENGROUP";
vDmeString += "&FIELD=GRP-END-DTE-01;GRP-END-DTE-02;GRP-END-DTE-03;GRP-END- DTE-04;";
vDmeString += "GRP-END-DTE-05;GRP-END-DTE-06;GRP-END-DTE-07;GRP-END-DTE-
08;GRP-END-DTE-09;";
vDmeString += "GRP-END-DTE-10;GRP-END-DTE-11;GRP-END-DTE-12;GRP-END-DTE-
13";
vDmeString += "&XCOLS=TRUE";
vDmeString += "&XKEYS=TRUE";
vDmeString += "&XRELS=TRUE";
vDmeString += "&XCOUNT=TRUE";
vDmeString += "&XIDA=TRUE";
vDmeString += "&OUT=XML";

// send the DME call to the server
var vDMEInfo = portalWnd.httpRequest(portalWnd.DMEPath + vDmeString);
if (!vDMEInfo || vDMEInfo.status)
{
var msg="Error calling DME, ";
msg += (vDMEInfo
? "(status code): "+vDMEInfo.status
: "bad server response.");
alert(msg);
return true;
}

// create an XML object to contain the DME data
var vObjDMEXML = new portalWnd.DataStorage(vDMEInfo);

// load a variable with the records returned by DME
var vRecords = vObjDMEXML.document.getElementsByTagName("RECORD");
if (vRecords.length == 0)
{
alert("No Dates Found");
return true;

}
var vCols = vRecords[0].getElementsByTagName("COL");
var SDate = lawForm.getFormValue("text85");
if (SDate != (vCols[0].firstChild.data ))
{
alert ("this is a test")
}


//alert ("Picked Date " + SDate)
//alert (vCols[0].firstChild.data )
//alert (vCols[1].firstChild.data )
//alert (vCols[2].firstChild.data )
//alert (vCols[3].firstChild.data )
//alert (vCols[4].firstChild.data )
//alert (vCols[5].firstChild.data )
//alert (vCols[6].firstChild.data )
//alert (vCols[7].firstChild.data )
//alert (vCols[8].firstChild.data )
//alert (vCols[9].firstChild.data )
//alert (vCols[10].firstChild.data )
//alert (vCols[11].firstChild.data )
//alert (vCols[12].firstChild.data )
//alert (vCols[13].firstChild.data )
return true;
}
}