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console 命令行工具 X clear

                    
>
console
 var canvas = document.getElementById("myCanvas");
    var ctx = canvas.getContext("2d");
    var ballRadius = 10;
    var x = canvas.width/2;
    var y = canvas.height-30;
    var dx = 2;
    var dy = -2;
    var paddleHeight = 10;
    var paddleWidth = 75;
    var paddleX = (canvas.width-paddleWidth)/2;
    var rightPressed = false;
    var leftPressed = false;
    document.addEventListener("keydown", keyDownHandler, false);
    document.addEventListener("keyup", keyUpHandler, false);
    function keyDownHandler(e) {
        if(e.keyCode == 39) {
            rightPressed = true;
        }
        else if(e.keyCode == 37) {
            leftPressed = true;
        }
    }
    function keyUpHandler(e) {
        if(e.keyCode == 39) {
            rightPressed = false;
        }
        else if(e.keyCode == 37) {
            leftPressed = false;
        }
    }
    function drawBall() {
        ctx.beginPath();
        ctx.arc(x, y, ballRadius, 0, Math.PI*2);
        ctx.fillStyle = "#0095DD";
        ctx.fill();
        ctx.closePath();
    }
    function drawPaddle() {
        ctx.beginPath();
        ctx.rect(paddleX, canvas.height-paddleHeight, paddleWidth, paddleHeight);
        ctx.fillStyle = "#0095DD";
        ctx.fill();
        ctx.closePath();
    }
function drawBricks(){
  ctx.beginPath();
ctx.rect(paddleX, canvas.height-paddleHeight, paddleWidth, paddleHeight);
  ctx.fillfillStyle="red"
  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 < ballRadius) {
            dy = -dy;
        }
        else if(y + dy > canvas.height-ballRadius) {
            if(x > paddleX && x < paddleX + paddleWidth) {
                dy = -dy;
            }
            else {
                clearInterval(game);
                alert("GAME OVER");
                document.location.reload();
            }
        }
        if(rightPressed && paddleX < canvas.width-paddleWidth) {
            paddleX += 7;
        }
        else if(leftPressed && paddleX > 0) {
            paddleX -= 7;
        }
        x += dx;
        y += dy;
    }

    var game = setInterval(draw, 10);
<canvas id="myCanvas" width="560" height="500"></canvas>