JS实现系统时间（自动）

<span id="DateTime">系统时间加载中...</span>

window.onload = function () {
//定时器每秒调用一次fnDate()
setInterval(function () {
fnDate();
}, 1000);
}

//js 获取当前时间
function fnDate() {
var oDiv = document.getElementById("DateTime");
var date = new Date();
var year = date.getFullYear();//当前年份
var month = date.getMonth();//当前月份
var data = date.getDate();//天
var hours = date.getHours();//小时
var minute = date.getMinutes();//分
var second = date.getSeconds();//秒
var time = year + "-" + fnW((month + 1)) + "-" + fnW(data) + " " + fnW(hours) + ":" + fnW(minute) + ":" + fnW(second);
var a = new Array("日", "一", "二", "三", "四", "五", "六");
var week = new Date().getDay();
var str = "星期" + a[week];
oDiv.innerHTML = time + "　" + str;
}
//补位 当某个字段不是两位数时补0
function fnW(str){return str > 9 ?  str :  "0" + str;}