一模一样的代码只是改成了显示系统时间为什么没有效果

Question

var WINDOW_WIDTH= 1024;var WINDOW_HEIGHT=768;var RADIUS=8;var MARGIN_TOP = 60;var MARGIN_LEFT = 30;var balls = [];const colors = ["#33B5E5","#0099CC","#AA66CC","#9933CC","#99CC00","#669900","#FFBB33","#FF8800","#FF4444","#CC0000"];window.onload=function(){ var canvas = document.getElementById('canvas'); var context = canvas.getContext("2d");   canvas.width =WINDOW_WIDTH;   canvas.height=WINDOW_HEIGHT;     setInterval(        function(){            render( context );            update();        }        ,        50    );}function update(){   var freshtime = new Date();   var freshseconds = freshtime.getSeconds();   var freshhours =freshtime.getHours();   var freshminutes =freshtime.getMinutes();   if (seconds!=freshseconds) {                if(parseInt(hours/10)!=parseInt(freshhours/10)){        addBalls(MARGIN_LEFT,MARGIN_TOP,parseInt(hours/10));        }        if( parseInt(hours%10) != parseInt(freshhours%10)){            addBalls( MARGIN_LEFT + 15*(RADIUS+1) , MARGIN_TOP , parseInt(hours/10) );        }        if( parseInt(minutes/10) != parseInt(freshminutes/10) ){            addBalls( MARGIN_LEFT + 39*(RADIUS+1) , MARGIN_TOP , parseInt(minutes/10) );        }        if( parseInt(minutes%10) != parseInt(freshminutes%10) ){            addBalls( MARGIN_LEFT + 54*(RADIUS+1) , MARGIN_TOP , parseInt(minutes%10) );        }         if( parseInt(seconds/10) != parseInt(freshseconds/10) ){            addBalls( MARGIN_LEFT + 78*(RADIUS+1) , MARGIN_TOP , parseInt(seconds/10) );        }        if( parseInt(seconds%10) != parseInt(freshseconds%10) ){            addBalls( MARGIN_LEFT + 93*(RADIUS+1) , MARGIN_TOP , parseInt(seconds%10) );        }        seconds=freshseconds;   }   updateBalls();}function updateBalls(){    for( var i = 0 ; i < balls.length ; i ++ ){        balls[i].x += balls[i].vx;        balls[i].y += balls[i].vy;        balls[i].vy += balls[i].g;        if( balls[i].y >= WINDOW_HEIGHT-RADIUS ){            balls[i].y = WINDOW_HEIGHT-RADIUS;            balls[i].vy = - balls[i].vy*0.75;        }    }}function addBalls( x , y , num ){    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 ){                var aBall = {                    x:x+j*2*(RADIUS+1)+(RADIUS+1),                    y:y+i*2*(RADIUS+1)+(RADIUS+1),                    g:1.5+Math.random(),                    vx:Math.pow( -1 , Math.ceil( Math.random()*1000 ) ) * 4,                    vy:-5,                    color: colors[ Math.floor( Math.random()*colors.length ) ]                }                balls.push( aBall )            }}function render(cxt){ cxt.clearRect(0,0,WINDOW_WIDTH, WINDOW_HEIGHT); var nowtime = new Date(); var hours =nowtime.getHours(); var minutes =nowtime.getMinutes(); var seconds = nowtime.getSeconds(); renderDigit(MARGIN_LEFT,MARGIN_TOP,parseInt(hours/10), cxt )    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);       for( var i = 0 ; i < balls.length ; i ++ ){        cxt.fillStyle=balls[i].color;        cxt.beginPath();        cxt.arc( balls[i].x , balls[i].y , RADIUS , 0 , 2*Math.PI , true );        cxt.closePath();        cxt.fill();    }}function renderDigit(x,y,num,cxt){ cxt.fillStyle="rgb(0,102,113)"; 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,y+i*2*(RADIUS+1)+(RADIUS+1),RADIUS,0,2*Math.PI) cxt.closePath() cxt.fill() }}