To get numbers of days in a month, use the getDate() method and get the days.
Example
You can try to run the following code to get a number of days in a month −
Live Demo
<!DOCTYPE html> <html> <body> <script> var days = function(month,year) { return new Date(year, month, 0).getDate(); }; document.write("Days in July: "+days(7, 2012)); // July month document.write("<br>Days in September: "+days(9, 2012)); // September Month </script> </body> </html>
Output
Days in July: 31 Days in September: 30