Find difference between 2 dates in JavaScript using format mm/dd/yyyy

jsdatediff1.js

var start_date = new Date('12/01/2013'),
    end_date   = new Date(),
    one_day_in_milliseconds = 1000*60*60*24,
    date_diff = Math.floor( ( end_date.getTime() - start_date.getTime() )/one_day_in_milliseconds ) ;
    
    console.log("Result 1 - Date difference between ",end_date, " & ",start_date, " - ", date_diff);

var s_date = new Date('2013-12-01'),
    date_diff_2 = Math.floor( ( end_date.getTime() - s_date.getTime() )/one_day_in_milliseconds ) ;
    
    console.log("Result 2 - Date difference between ",end_date, " & ",s_date, " - ", date_diff_2);