カウントダウンをクラスの切り替えで

countdown.js

$(function() {
	var limit  = new Date("Feb 1,2016 00:00:00"),
			$times = [
				$('#date10'),   $('#date01'),
				$('#hour10'),   $('#hour01'),
				$('#minute10'), $('#minute01'),
				$('#second10'), $('#second01')
			];

	var updateTime = function(timeArray) {
		if ( $times.length !== timeArray.length ) return;
		
		for ( var i = 0, length = timeArray.length; i < length; i++ ) {
			if ( ! $times[i].hasClass('num' + timeArray[i]) ) {
				$times[i].removeClass(function(index, className) {
					return (className.match(/num\d/) || []).join(' ');
				}).addClass('num' + timeArray[i]);
			}
		}
	};

	setInterval(function() {
		var now  = new Date(),
				left = limit - now,
				day  = 24 * 60 * 60 * 1000,
				d    = Math.floor(left / day),
				h    = Math.floor((left % day) / (60 * 60 * 1000)),
				m    = Math.floor((left % day) / (60 * 1000)) % 60,
				s    = Math.floor((left % day) / 1000) % 60;

		updateTime([
			Math.floor(d / 10), d % 10,
			Math.floor(h / 10), h % 10,
			Math.floor(m / 10), m % 10,
			Math.floor(s / 10), s % 10,
		]);
	}, 1000);
});