js get a simple example of the last day date of a certain month

//Get the last day of a certain month
        function getLastDay(year,month) {        
var new_year = year;    //Take the current year
var new_month = month++;//Pick the first day of the next month for easy calculation (the last day is not fixed)
             if(month>12) {        
new_month -=12;          // Month reduction
new_year++;
             }        
var new_date = new Date(new_year,new_month,1);                                                                                                                    �
return (new Date(new_date.getTime()-1000*60*60*24)).getDate();//Get the last day date of the month
        }