如何实现点击数字文本<a>元素时获取有效上下文的JavaScript功能

function getContext(id) {
  const targetEl = document.getElementById(id);
  if (!targetEl) return ''; // 没找到元素直接返回空，避免报错

  const validTags = ['A', 'BR']; // 注意DOM的tagName是大写的
  const contextNodes = [];

  // 往前找2个有效节点
  let prevEl = targetEl.previousElementSibling;
  let prevCount = 0;
  while (prevEl && prevCount < 2) {
    if (validTags.includes(prevEl.tagName)) {
      contextNodes.unshift(prevEl); // 往前找的节点要插在数组前面，保证顺序正确
      prevCount++;
    }
    prevEl = prevEl.previousElementSibling;
  }

  // 加入当前点击的元素，用加粗标记
  contextNodes.push(targetEl);

  // 往后找2个有效节点
  let nextEl = targetEl.nextElementSibling;
  let nextCount = 0;
  while (nextEl && nextCount < 2) {
    if (validTags.includes(nextEl.tagName)) {
      contextNodes.push(nextEl);
      nextCount++;
    }
    nextEl = nextEl.nextElementSibling;
  }

  // 把节点转成HTML字符串，拼接起来
  return contextNodes.map(node => {
    return node === targetEl ? `<b>${node.outerHTML}</b>` : node.outerHTML;
  }).join(' ');
}

function getContext(id) {
  const targetEl = document.getElementById(id);
  if (!targetEl) return '';

  const allWords = Array.from(document.getElementsByTagName('a'));
  const targetPos = allWords.indexOf(targetEl);
  if (targetPos === -1) return '';

  // 计算前后的范围，防止越界
  const start = Math.max(0, targetPos - 2);
  const end = Math.min(allWords.length - 1, targetPos + 2);

  // 提取上下文，当前元素加粗
  return allWords.slice(start, end + 1).map((word, idx) => {
    return idx === targetPos - start ? `<b>${word.outerHTML}</b>` : word.outerHTML;
  }).join(' ');
}