$(document).ready(function(){

    var weeknumber = moment(12-25-1995, MM-DD-YYYY).week();

    console.log(weeknumber);

  });

According momentjs docs:

Because different locales define week of year numbering differently,
Moment.js added moment#week to get/set the localized week of the year.

The week of the year varies depending on which day is the first day of
the week (Sunday, Monday, etc), and which week is the first week of
the year.

For example, in the United States, Sunday is the first day of the
week. The week with January 1st in it is the first week of the year.

So, if you are having problems getting the right week number use .isoWeek()

$(document).ready(function(){

  var weeknumber = moment(11-26-2016, MMDDYYYY).isoWeek();

  alert(weeknumber);

});

Example