為啥我的是向前加一秒？

var?RADIUS?=?8;
var?MARGIN_LEFT=60;
var?MARGIN_TOP=30;
const?endTime?=?new?Date(2017,8,19,13,07,52);
var?showtime=0;
var?ball?=?{x:512,y:100,r:20,g:2,vx:-4,vy:0,color:"#005588"};
var?balls?=?[];
const?colors?=?["#33B5E5","#0099CC","#AA66CC","#9933CC","#99CC00","#669900","#FFBB33","#FF8800","#FF4444","#CC0000"];
window.onload=function(){
	var?c=?document.getElementById("canvas");
	var?ctx?=?c.getContext("2d");
	showtime=getsecond();
	?setInterval(
????????function(){
????????	drawball(ctx);
????????????render(ctx);
????????????update();
????????},50)
}
function?update(){
	var?nextsecond=getsecond();
??var?nextHours?=?parseInt(?nextsecond?/?3600);
????var?nextMinutes?=?parseInt(?(nextsecond?-?nextHours?*?3600)/60?)
????var?nextSeconds?=?nextsecond?%?60

????var?curHours?=?parseInt(?showtime?/?3600);
????var?curMinutes?=?parseInt(?(showtime?-?curHours?*?3600)/60?)
????var?curSeconds?=?showtime?%?60

????if(?nextSeconds?!=?curSeconds?){

????????showtime?=?nextsecond;
????}
}
function?getsecond(){
	var?curTime?=?new?Date();
	var?ret?=?curTime.getTime()-endTime.getTime();
	ret?=?Math.round(ret/1000);
	return?ret>=0?ret:0;
}
function?drawball(ctx){
	ctx.clearRect(0,0,1024,768);
	ctx.beginPath();
	ctx.fillStyle=ball.color;
	ctx.arc(ball.x,ball.y,ball.r,0,2*Math.PI);
	ctx.fill();
}
function?render(ctx){

	var?hours=parseInt(showtime/3600);
	var?minutes=parseInt((showtime-hours*3600)/60);
	var?seconds=parseInt(showtime%60);
	renderDigit(MARGIN_LEFT,MARGIN_TOP,parseInt(hours/10),ctx);
	renderDigit(MARGIN_LEFT+15*(RADIUS+1),MARGIN_TOP,parseInt(hours%10),ctx);
	renderDigit(MARGIN_LEFT+30*(RADIUS+1),MARGIN_TOP,10,ctx);
	renderDigit(MARGIN_LEFT+39*(RADIUS+1),MARGIN_TOP,parseInt(minutes/10),ctx);
	renderDigit(MARGIN_LEFT+54*(RADIUS+1),MARGIN_TOP,parseInt(minutes%10),ctx);
	renderDigit(MARGIN_LEFT+69*(RADIUS+1),MARGIN_TOP,10,ctx);
	renderDigit(MARGIN_LEFT+78*(RADIUS+1),MARGIN_TOP,parseInt(seconds/10),ctx);
	renderDigit(MARGIN_LEFT+93*(RADIUS+1),MARGIN_TOP,parseInt(seconds%10),ctx);
}
function?renderDigit(x,y,num,ctx){
	ctx.fillStyle="rgb(0,102,153)";
	for(var?i=0;i<digit[num].length;i++){
		for(var?j=0;j<digit[num][i].length;j++){
			if?(digit[num][i][j]==1){
				ctx.beginPath();
				ctx.arc(x+j*2*(RADIUS+1)+(RADIUS+1),y+i*2*(RADIUS+1)+(RADIUS+1),RADIUS,0,2*Math.PI);
				ctx.closePath();
				ctx.fill();
			}
		}
	}
}