how to get the number of days in a month in javascript

 // instantiate a date object
 var dt = new Date();

// dt.getMonth() will return a month between 0 - 11
// we add one to get to the last day of the month 
// so that when getDate() is called it will return the last day of the month
 var month = dt.getMonth() + 1;
 var year = dt.getFullYear();

// this line does the magic (in collab with the lines above)
 var daysInMonth = new Date(year, month, 0).getDate(); var dt = new Date();
 var month = dt.getMonth();
 var year = dt.getFullYear();
daysInMonth = new Date(year, month, 0).getDate();