difference between 2 dates in days months years in javascript code example

Example: javascript after 2 months date find

var newDate = new Date(date.setMonth(date.getMonth()+8));

var jan312009 = new Date(2009, 0, 31);
var eightMonthsFromJan312009  = jan312009.setMonth(jan312009.getMonth()+8);
//@SUJAY