Javascript (Node.js) function for getting last working/business day of the month.

last_business_day_of_month.js

/**
 * Finds last working/business day of the month. 
 * 
 * Not tested for cross-browser compability. Works in Node.js though.
 * 
 * EXAMPLES:
 * 
 * 1. Returns last day of the last month of the current year:
 * 
 * var result = lastBusinessDayOfMonth();
 * 
 * 2. Returns last day of the current month of the current year:
 * 
 * var date = new Date();
 * var year = date.getFullYear();
 * var month = date.getMonth() + 1;
 *
 * if (12 === month) {
 *     month = 0;
 *     year++;
 * }
 *
 * var result = lastBusinessDayOfMonth(year, month);  
 * 
 * @param year Provide null for current year, provide xxxx for custom year.
 * @param month Provide null for current month, provide 0-11 for custom month.
 *
 * @returns object Date A resulting date object of the last working/business day of the month.
 */
function lastBusinessDayOfMonth(year, month) {
    var date = new Date();
    var offset = 0;
    var result = null;
    
    if ('undefined' === typeof year || null === year) {
        year = date.getFullYear();
    }
    
    if ('undefined' === typeof month || null === month) {
        month = date.getMonth();
    }

    do {
        result = new Date(year, month, offset);
        
        offset--;
    } while (0 === result.getDay() || 6 === result.getDay());

    return result;
}