javascipt函数调用过程和值传递

Question

 <canvas id="canvas" style="border: 1px solid red ;" ></canvas>
    <script type="text/javascript">
        var ball={x:512, y:100, r:20, g:2, vx:-4, vy:4, color:"#00FFFF"}//g重力加速度，
        window.onload=function(){
        var canvas=document.getElementById("canvas");
        canvas.width=768;
        canvas.height=768;
        var context=canvas.getContext("2d");
         setInterval(function(){
            render(context);
            update();},50)

}
function update(){
    ball.x =ball.x+ball.vx;
    ball.y =ball.y+ball.vy;
    ball.vy =ball.vy+ball.g;

    if(ball.y>=768-ball.r)、
    //请问这里的条件成立后，ball.y和ball.vy的值是值传递的吗?
    //两个ball.y和ball.vy传递之后，每调用update()方法是怎样是怎样的执行过程？
    {
        ball.y=768-ball.r;
        ball.vy=-ball.vy;

    }


}
function render(cxt){
    cxt.clearRect(0,0,cxt.canvas.height,cxt.canvas.height);
    cxt.fillStyle=ball.color;
    cxt.beginPath();
    cxt.arc(ball.x,ball.y,ball.r,0,2*Math.PI);
    cxt.closePath();
    cxt.fill();

}
    </script>

Answer 1

ball对于函数来说，是闭包变量，可以理解为全局变量，不是值传递。