如何使用JavaScript在浏览器中绘制并标注三角形？

// 创建画布元素
const canvas = document.createElement('canvas');
canvas.width = 400;
canvas.height = 400;
document.body.appendChild(canvas);
const ctx = canvas.getContext('2d');

// 三角形顶点坐标
const A = { x: 50, y: 300 };
const B = { x: 250, y: 300 };
const C = { x: 150, y: 100 };

// 计算边长
function distance(p1, p2) {
  return Math.sqrt(Math.pow(p2.x - p1.x, 2) + Math.pow(p2.y - p1.y, 2));
}
const AB = distance(A, B);
const BC = distance(B, C);
const CA = distance(C, A);

// 计算角度（弧度转角度）
function angle(p1, p2, p3) {
  const a = distance(p2, p3);
  const b = distance(p1, p3);
  const c = distance(p1, p2);
  return Math.acos((a * a + b * b - c * c) / (2 * a * b)) * 180 / Math.PI;
}
const angleA = angle(B, A, C);
const angleB = angle(C, B, A);
const angleC = angle(A, C, B);

// 绘制三角形
ctx.beginPath();
ctx.moveTo(A.x, A.y);
ctx.lineTo(B.x, B.y);
ctx.lineTo(C.x, C.y);
ctx.closePath();
ctx.stroke();

// 标注边长和角度
ctx.font = "14px Arial";
ctx.fillText(`AB = ${AB.toFixed(2)}`, (A.x + B.x) / 2, (A.y + B.y) / 2 + 20);
ctx.fillText(`BC = ${BC.toFixed(2)}`, (B.x + C.x) / 2, (B.y + C.y) / 2 + 20);
ctx.fillText(`CA = ${CA.toFixed(2)}`, (C.x + A.x) / 2, (C.y + A.y) / 2 + 20);
ctx.fillText(`∠A = ${angleA.toFixed(2)}°`, A.x - 20, A.y - 20);
ctx.fillText(`∠B = ${angleB.toFixed(2)}°`, B.x, B.y - 20);
ctx.fillText(`∠C = ${angleC.toFixed(2)}°`, C.x, C.y + 30);