const canvas = document.getElementById("canvas");
  const cxt = canvas.getContext("2d");
  cxt.beginPath();
  cxt.moveTo(10, 10);
  cxt.lineWidth = 20;
  // 末端以圆形结束
  cxt.lineCap = "round";
  cxt.lineTo(50, 50);
  cxt.stroke();
  cxt.closePath();

  cxt.beginPath();
  cxt.moveTo(80, 50);
  cxt.lineTo(100, 100);
  cxt.lineWidth = "20";
  cxt.lineCap = "butt";
  cxt.stroke();

  cxt.beginPath();
  cxt.moveTo(150, 20);
  cxt.lineTo(130, 130);
  cxt.lineWidth = "20";
  cxt.lineCap = "square";
  cxt.stroke();