先画条直线,如下:    <canvas id="myCanvas" width="1000" height="800"></canvas>
    <script>
      var canvas = document.getElementById('myCanvas');
      var context = canvas.getContext('2d');      context.beginPath();
      context.lineWidth="2"
      context.strokeStyle="black"
      context.moveTo(10, 10);
      context.lineTo(100, 100);
      context.stroke();
    </script>不用clearRect(),怎么删除这条直线?htmlcanvas2d