SOURCE

    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() {
        ctx.clearRect(0, 0, canvas.width, canvas.height);
        drawBall();
      drawPaddle();
        if(x + dx > canvas.width-ballRadius || x + dx < ballRadius) {
            dx = -dx;
        }
        if(y + dy > canvas.height-ballRadius || y + dy < ballRadius) {
            dy = -dy;
        }
        if(rightPressed && paddleX < canvas.width-paddleWidth) {
            paddleX += 7;
        }
        else if(leftPressed && paddleX > 0) {
            paddleX -= 7;
        }
        x += dx;
        y += dy;
    }    
    setInterval(draw, 10);

        
        
        
        
        
        
        
        
        
        
        
        
        
        
        

<canvas id="myCanvas" width="480" height="320"></canvas>