dateDifference_FF.js

$( document ).ready(function() {
    
    var placeholder = 'result';    // Give your result fields class name
    var date_one = 'start_date';   // Give your Start Day fields class name
    var date_two = 'end_date';  // Give your End Day fields class name
    var format = 'mm.dd.yyyy';   // Give your Date Format  (use mm for m, dd for d and yyyy for y)
    var seperator = "."      // Give your date seperator here
    var date = format.split(seperator);
  
    
    var dateObj = {
        d:date.indexOf('dd'),
        m:date.indexOf('mm'),
        y:date.indexOf('yyyy'),
    };
    
    $('.'+date_two+' , .'+date_one).change(function(){
       
        var date_in = $('.'+ date_one).val().split(seperator);
        var date_out = $('.'+date_two).val().split(seperator);
   
        var date1 = new Date(date_in[dateObj.m]+seperator+date_in[dateObj.d]+seperator+date_in[dateObj.y]);
        var date2 = new Date(date_out[dateObj.m]+seperator+date_out[dateObj.d]+seperator+date_out[dateObj.y]);
        
        const diffTime = Math.abs(date2 - date1);
        const diffDays = Math.ceil(diffTime / (1000 * 60 * 60 * 24)); 
        
        if(!isNaN(diffDays)){
             $('.'+placeholder).val(diffDays).trigger("change");
        }
       
    })

});