Compare the duration of dates with selected dropdown value...read please

I have the Drop down with values as "One year ", "Two year",...etc.. Ok? also i have two ajax textbox with calender extender . I want to popup alert message if dropdown selected value is "One year" and 开发者_如何学Cduration between the both textbox value Means dates not matches. getting what i mean ? please help me.

Algorithm :
1.Get the both date from the text box.
2. The find the epcoch time for each date. //
3. subtract the both dates.
4. subtract_result = 365*24*60*60  // Finding the 1 year timestamp values
5. So, it the difference exceed than above calculation , you could sure that the date is mis matching.
 


    // This is for first date
    first = new Date(2010, 03, 08, 15, 30, 10); // Get the first date epoch object
   // document.write((first.getTime())/1000); // get the actual epoch values
    second = new Date(2012, 03, 08, 15, 30, 10); // Get the first date epoch object
    //document.write((second.getTime())/1000); // get the actual epoch values
    diff= second - first ;
    one_day_epoch = 24*60*60 ;  // calculating one epoch
    if ( diff/ one_day_epoch > 365 ) // check , is it exceei
    {
    alert( 'date is exceeding one year');
    }