帮我看看countdown.js代码，对比没有问题啊，显示一直是00:00:00呢，当前日期是：2016/1/19。

var WINDOW_WIDTH =1024;
var WINDOW_HEIGHT = 768;
var RADIUS =8;
var MARGIN_TOP=60;
var MARGIN_LEFT=30;
const endTime =new Date(2016,0,17,15,47,52);
var curShowTimeSeconds = 0;
window.onload = function(){
    var canvas = document.getElementById("canvas");
    var cxt =canvas.getContext("2d");

    canvas.width =WINDOW_WIDTH;
    canvas.height = WINDOW_HEIGHT;
    curShowTimeSeconds =getCurrentShowTimeSeconds()
    render(cxt)
 }
function getCurrentShowTimeSeconds(){

    var curTime = new Date();
    var ret = endTime.getTime() - curTime.getTime();
    ret = Math.round( ret/1000 )

    return ret >= 0 ? ret : 0;}

function render(cxt){
      var hours = parseInt( curShowTimeSeconds / 3600);
    var minutes = parseInt( (curShowTimeSeconds - hours * 3600)/60 )
    var seconds = curShowTimeSeconds % 60 ;

     renderDigit(MARGIN_LEFT,MARGIN_TOP,parseInt(hours/10),cxt)
     renderDigit(MARGIN_LEFT+15*(RADIUS+1),MARGIN_TOP,parseInt(hours%10),cxt)
     renderDigit(MARGIN_LEFT+30*(RADIUS+1),MARGIN_TOP,10,cxt)     
     renderDigit(MARGIN_LEFT+39*(RADIUS+1),MARGIN_TOP,parseInt(minutes/10),cxt)
     renderDigit(MARGIN_LEFT+54*(RADIUS+1),MARGIN_TOP,parseInt(minutes%10),cxt)
     renderDigit(MARGIN_LEFT+69*(RADIUS+1),MARGIN_TOP,10,cxt)

     renderDigit(MARGIN_LEFT+78*(RADIUS+1),MARGIN_TOP,parseInt(seconds/10),cxt)
     renderDigit(MARGIN_LEFT+93*(RADIUS+1),MARGIN_TOP,parseInt(seconds%10),cxt)
 }

 function renderDigit(x,y,num,cxt){
     cxt.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){
                 cxt.beginPath();
                 cxt.arc(x+j*2*(RADIUS+1)+(RADIUS+1),y+i*2*(RADIUS+1)+(RADIUS+1),RADIUS,0,2*Math.PI)
                 cxt.closePath()
                 cxt.fill()
             }


 }