Date difference in Javascript

This can be a need of people that they get instant difference between two dates without the postback. In .Net (C# or VB .Net) its pretty much easy and straight but in Javascript its not that much straight (Though is easy).
Anyways here is the solution. Following is the Javascript function calculating date difference in between two dates (give in two textbox named txtStartDate and txtEndDate) and will store the result (in days) in a textbox named txtDuration.

function calculateDuration()
{
var msInDay = 1000 * 60 * 60 * 24; //Milliseconds in a day
var startDateMS = new Date(document.getElementById("txtStartDate").value).getTime();
var endDateMS = new Date(document.getElementById("txtEndDate").value).getTime();
var differenceMS = Math.abs(endDateMS - startDateMS);
document.getElementById("txtDuration").value = Math.round(differenceMS/msInDay);
}

This function can be called like
<asp:TextBox ID="txtDuration" runat="server" onclick="javascript:calculateDuration();" onfocus="javascript:calculateDuration();"></asp:TextBox>

Calling a Server side function from Javascript

Many of us needs a server side function to be called from JavaScript. We can do this easily using __doPostBack

as

Javascript Code

function CallServerCode()

{

__doPostBack('btnTest', '');

}

and in HTML

<­button type="­button" onclick="javascript:CallServerCode();">Call Server Code<­/­button­>

<­asp­:­linkbutton id="btnTest" runat="server" text="ASP .Net Button"­> <­/­asp­:­linkbutton>

and the Server side code

Protected Sub btnHidden_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnTest.Click

Response.Write("Hello")

End Sub

Now note that whenever the client button with caption "Call Server Code" will be clicked it will call Serverside event of btnTest using Javascript.