其中删除小球那块儿代码把括号补全是怎么样的呢 都试过了也不对呀

var cnt = 0

    for( var i = 0 ; i < balls.length ; i ++ )

        if( balls[i].x + RADIUS > 0 && balls[i].x -RADIUS < WINDOW_WIDTH )

            balls[cnt++] = balls[i]

    while( balls.length > cnt ){

        balls.pop();

    }

    console.log(balls.length);