<canvas id="canvas" width="100px" height="100px"></canvas>
#canvas {
  border: 1px solid #ccc
}
const canvas = document.getElementById("canvas");
const cxt = canvas.getContext("2d");
// 开始绘制路径：得到绘制命令
cxt.beginPath();

// 路径的起点
cxt.moveTo(20, 30);

// 绘制直线
cxt.lineTo(45, 50);
cxt.lineTo(30, 80);

// 填充路径，自动闭合 
cxt.fill();

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External JavaScript

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