How to compare two date in javascript

var sDate = document.getElementById("textboxStartDate").value; //start date

var TDate = document.getElementById("textboxHDate").value; //today date

var frmDate = new Date(sDate);

var TodayDate = new Date(TDate);

if(frmDate <= TodayDate)

{

alert('Start Date not be less than todays date.');

document.getElementById("txtStartDate").focus();

return false;

}