Get the number of days in a month in javascript.

daysInMonth.js

/**
 * Get the number of days in a month in javascript.
 *
 * Ref:
 *  http://stackoverflow.com/questions/315760/what-is-the-best-way-to-determine-the-number-of-days-in-a-month-with-javascript
 */
function daysInMonth(year, month) {
    var now = new Date;

    month = typeof month != undefined ? month
            : (typeof year != undefined ? year : now.getMonth() + 1);

    year = typeof month != undefined && typeof year != undefined ? year
            : now.getFullYear();

    now.setFullYear(year, month, 0);
    return now.getDate();
}