SOURCE

function getNowFormatDate() {
    var date = new Date();
    var seperator1 = "-";
    var seperator2 = ":";
    var month = date.getMonth() + 1;
    var strDate = date.getDate();
  	var seconds=date.getSeconds();
    if (month >= 1 && month <= 9) {
        month = "0" + month;
    }
    if (strDate >= 0 && strDate <= 9) {
        strDate = "0" + strDate;
    }
  	if(seconds<=9){
      	seconds="0"+seconds;
    }
    var currentdate = date.getFullYear() + seperator1 + month + seperator1 + strDate
            + " " + date.getHours() + seperator2 + date.getMinutes()
            + seperator2 + seconds;
    return currentdate;
}

function chanP(){
	var t=getNowFormatDate();
	$("p").html(t); 
}
var int=self.setInterval("chanP()",50);

<p>time</p>