This uses moment.js to select the date of the next Leamington Geeks meetup. It chooses either the 3rd Tuesday of the month if it's December or the last Tuesday of the month if it's any other month. If that date has passed, it adds a month and starts the process again. Is this the best way to do that?

usingmoment.js

var today = moment(new Date()),
    monthEnd,
    nextDate;

do {
    if (monthEnd === undefined) {
        monthEnd = moment(new Date());
    }
    else {
        monthEnd = monthEnd.add('months', 1);
    }
    if (monthEnd.month() == 11) {
        // If it's December, choose the 3rd Tuesday
        nextDate = monthEnd.startOf('month').startOf('week').add('days', 2).add('weeks', 2);
    }
    else {
        // Choose the last Tuesday
        nextDate = monthEnd.EndOf('month').subtract('days', Math.abs((2 - monthEnd.weekday() - 7) % 7));
    }
} while (nextDate.isBefore(today));