How to do the date difference using javascript?

I have two textboxes i want to calculate the year difference between two Dates.

function CalcalationofDATE()

{

//getting the dates from textboxes

var Date1 = document.getElementById('txtDate.CLIENTID').value;

var Date2 = document.getElementById(' txtDate1.CLIENTID').value;

//if the dates are not there empty asign value

if (Date1 == "" || Date2 == "")

{

document.getElementById('txtdateDiff').innerHTML = "";

}

else

{

var dt1 = new Date(Date1);

var dt2 = new Date(Date12);

var dtVal = dt1.getFullYear() - dt2.getFullYear();

document.getElementById('txtdatediff').innerHTML = dtVal;

}

}