SOURCE

console 命令行工具 X clear

                    
>
console
var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");
var x=canvas.width/2;
var y=canvas.height-30;
var dx=2;
var dy=-2;
function drawBall(){
ctx.beginPath();
ctx.arc(x,y,10,0,Math.PI*2);
ctx.fillStyle="#0095DD";
ctx.fill();
ctx.closePath();
}
function draw(){
  drawBall();
  x+=dx;
  y+=dy;
}
setInterval(draw,10);
<canvas id="myCanvas" width="480" height="320"></canvas>