Edit in JSFiddle

(function(global) {
	var container = document.getElementById('clock-block'),
		getTime, revise, showTime, second;

	// 显示时间,刷新频率是1s
	showTime = function showTime() {
		var dateObj = new Date(),
			currentSecond = dateObj.getSeconds(),
			arr= [];

		if (second !== currentSecond) {
			arr.push(dateObj.getHours());
			arr.push(dateObj.getMinutes());
			arr.push(currentSecond);

			container.innerHTML = arr.join(':');
			second !== currentSecond;
		}
		setTimeout(showTime, 100);
	};
	showTime();

})(window);
<div id="clock-block"></div>