function diff_weeks(dt2, dt1)   
 {  
  
  var diff =(dt2.getTime() - dt1.getTime()) / 1000;  
  diff /= (60 * 60 * 24 * 7);  
  return Math.abs(Math.round(diff));  
    
 }  
  
dt1 = new Date(2014,10,2);  
dt2 = new Date(2014,10,11);  
console.log(diff_weeks(dt1, dt2));  
  
dt1 = new Date("June 13, 2014 08:11:00");  
dt2 = new Date("October 19, 2014 11:13:00");  
console.log(diff_weeks(dt1, dt2));