canvas元素运动碰撞的小方块

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>方块运动碰撞</title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }

        #canvas {
            border: 1px solid red;
        }
    </style>
</head>

<body>
    <canvas id="canvas">您的浏览器不支持canvas，请升级</canvas>
    <script>
        let canvas = document.getElementById('canvas');
        let ctx = canvas.getContext('2d');//获取画笔对象
        
        let width=500,height=400,w=50,h=50,fillStyle='red',xFlag=1,yFlag=1,step=2,x=0,y=0;
        // xFlag 1 :正方向 往右走  否则为0
        // yFlag 1 :正方向 往下走  否则为0
        canvas.width=width;
        canvas.height=height;

        let maxX=width-w;//最大的x位置
        let maxY=height-h;//最大的y位置

        setInterval(()=>{
            // 每一次执行前都清空画布
            ctx.clearRect(0,0,width,height);
            // 判断方向
            if(xFlag == 1){
                x+=step;
                if(x>=maxX){
                    xFlag=0;
                }
            }else if(xFlag == 0){
                x += -step;
                if(x<=0){
                    xFlag=1;
                }
            }
            // 判断方向
            if(yFlag == 1){
                y+=step;
                if(y>=maxY){
                    yFlag=0;
                }
            }else if(yFlag == 0){
                y += -step;
                if(y<=0){
                    yFlag=1;
                }
            }

            ctx.beginPath();
            ctx.fillStyle=fillStyle;
            ctx.fillRect(x,y,w,h);
        },30)
    </script>
</body>

</html>