javascript 以“年-月-日时：分：秒”格式显示当前时间

/**
 * Created by shgbit on 2015/1/9.
 *js代码
 */
function showNow(){

var t=new Date();
var month=t.getMonth()+1<10? '0'+(t.getMonth()+1):t.getMonth()+1;
var date=t.getDate()<10? '0'+t.getDate():t.getDate();
var hour=t.getHours()<10 ? '0'+t.getHours():t.getHours();
var minutes=t.getMinutes()<10 ? '0'+t.getMinutes():t.getMinutes();
var seconds=t.getSeconds()<10 ? '0'+t.getSeconds():t.getSeconds();
return t.getFullYear()+'-'+ month+'-'+date +' '+hour +':'+ minutes+':'+ seconds;

}

<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <script type="text/javascript" src="https://files.cnblogs.com/greenteaone/tddd.js" ></script>
    <title>显示当前时间</title>
</head>
<body>
 <label id="test">hh</label>
 <script type="text/javascript">
    window.onload=function(){
        test();
        setInterval(test,1000)
    };
     function test(){
         document.getElementById('test').innerText=showNow();
     }
 </script>
</body>
</html>