数组长度不断增加，运行越来越慢
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-RANIUS){
balls[i].y=WINDOW_HEIGHT-RANIUS;
balls[i].vy=-balls[i].vy*0.75;
}
if(balls[i].x>WINDOW_WIDTH+RANIUS||balls[i].x<-RANIUS){
balls.splice(i,1);
} // 从balls数组中移除跳出画布的小球
}
console.log(balls.length);
}
