如何利用JavaScript开发网页画板功能

<!DOCTYPE html>
<html>
<head>
  <title>如何利用JavaScript开发网页画板功能</title>
</head>
<body>
  <canvas id="canvas" width="800" height="600"></canvas>
  <script>
    var canvas = document.getElementById('canvas');
	var context = canvas.getContext('2d');
	var isDrawing = false;
	var lastX = 0;
	var lastY = 0;
	 
	function startDrawing(e) {
	  isDrawing = true;
	  lastX = e.clientX;
	  lastY = e.clientY;
	}
	 
	function draw(e) {
	  if (!isDrawing) return;
	  context.beginPath();
	  context.moveTo(lastX, lastY);
	  context.lineTo(e.clientX, e.clientY);
	  context.stroke();
	  lastX = e.clientX;
	  lastY = e.clientY;
	}
	 
	function stopDrawing() {
	  isDrawing = false;
	}
	 
	canvas.addEventListener('mousedown', startDrawing);
	canvas.addEventListener('mousemove', draw);
	canvas.addEventListener('mouseup', stopDrawing);
  </script>
</body>
</html>

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