CanvasRenderingContext2D：drawFocusIfNeeded() 方法

drawFocusIfNeeded(element)
drawFocusIfNeeded(path, element)

<canvas id="canvas">
  <button id="button1">继续</button>
  <button id="button2">退出</button>
</canvas>

const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");
const button1 = document.getElementById("button1");
const button2 = document.getElementById("button2");

document.addEventListener("focus", redraw, true);
document.addEventListener("blur", redraw, true);
canvas.addEventListener("click", handleClick, false);
redraw();

function redraw() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  drawButton(button1, 20, 20);
  drawButton(button2, 20, 80);
}

function handleClick(e) {
  // 计算点击坐标
  const x = e.clientX - canvas.offsetLeft;
  const y = e.clientY - canvas.offsetTop;

  // 如果合适，聚焦 button1
  drawButton(button1, 20, 20);
  if (ctx.isPointInPath(x, y)) {
    button1.focus();
  }

  // 如果合适，聚焦 button2
  drawButton(button2, 20, 80);
  if (ctx.isPointInPath(x, y)) {
    button2.focus();
  }
}

function drawButton(el, x, y) {
  const active = document.activeElement === el;
  const width = 150;
  const height = 40;

  // 按钮背景
  ctx.fillStyle = active ? "pink" : "lightgray";
  ctx.fillRect(x, y, width, height);

  // 按钮文本
  ctx.font = "15px sans-serif";
  ctx.textAlign = "center";
  ctx.textBaseline = "middle";
  ctx.fillStyle = active ? "blue" : "black";
  ctx.fillText(el.textContent, x + width / 2, y + height / 2);

  // 定义可点击区域
  ctx.beginPath();
  ctx.rect(x, y, width, height);

  // 如果合适，绘制焦点环
  ctx.drawFocusIfNeeded(el);
}