绘制线条

// Get the context
context = document.getElementById("cvs").getContext(‘2d‘);

// Anti aliasing fix. This makes the lines look crisp and sharp and means that rounding to the
// nearest half pixel is not needed. If you don‘t mind slightly thicker lines you can do without this
context.translate(0.5, 0.5);

// Draw the circle
context.beginPath();
context.setLineDash([5]);
context.arc(65, 65, 50, 0, 2 * Math.PI, false);
context.stroke();

// Draw the square
context.beginPath();
context.setLineDash([5, 2]);
context.rect(130, 15, 100, 100);
context.stroke();

// Draw the triangle
context.beginPath();
context.setLineDash([1, 2]);
context.moveTo(245, 115);
context.lineTo(295, 15);
context.lineTo(345, 115);
context.closePath();
context.stroke();

// Draw the irregular shape
context.beginPath();
context.fillStyle = ‘#eee‘;
context.setLineDash([15]);
context.moveTo(360, 115);
context.lineTo(375, 95);
context.lineTo(405, 15);
context.lineTo(445, 65);
context.lineTo(445, 115);
context.closePath();
context.fill();
context.stroke();