Compare two dates in javascript

var yearDiff = 100;   
var d = new Date();
    var year = d.getFullYear();
    var month = d.getMonth();
    var day = d.getDate();
    var dtToday = new Date(year - yearDiff , month, day)

    mydate = new Date(DOBDate);
    year = mydate.getFullYear();
    month = mydate.getMonth();
    day = mydate.getDate();
    mydate = new Date(year, month, day);

    if (mydate > dtToday) {
      alert("Age can not be greater than 100 years.");
    }
    else {
        alert("Prev Smaller");
    }