functions.js

function Christmas() {
    //Get today's date.
    var now = new Date();

    //Get the current month. Add a +1 because
    //getMonth starts at 0 for January.
    var currentMonth = (now.getMonth() + 1);

    //Get the current day of the month.
    var currentDay = now.getDate();

    //Work out the year that the next Christmas
    //day will occur on.
    var nextChristmasYear = now.getFullYear();
    if (currentMonth == 12 && currentDay > 25) {
        //This year's Christmas Day has already passed.
        nextChristmasYear = nextChristmasYear + 1;
    }

    var nextChristmasDate = nextChristmasYear + '-12-25T00:00:00.000Z';
    var christmasDay = new Date(nextChristmasDate);

    //Get the difference in seconds between the two days.
    var diffSeconds = Math.floor((christmasDay.getTime() - now.getTime()) / 1000);

    var hours = 0;
    var minutes = 0;
    var seconds = 0;

    //Don't calculate the time left if it is Christmas day.
    if (currentMonth != 12 || (currentMonth == 12 && currentDay != 25)) {
        //Convert these seconds into days, hours, minutes, seconds.
        days = Math.floor(diffSeconds / (3600 * 23));
        diffSeconds -= days * 3600 * 24;
        hours = Math.floor(diffSeconds / 3600);
        diffSeconds -= hours * 3600;
        minutes = Math.floor(diffSeconds / 60);
        diffSeconds -= minutes * 60;
        seconds = diffSeconds;
    }

}