如何找到当前页面中出现次数最多的HTML标签

> document.querySelectorAll('*')
< NodeList(593) [html, head, meta, meta, meta, meta, meta, meta, meta, title, link#favicon, link, link#MainCss, link#mobile-style, link, link, link, script, script, script, script, script, script, script, link, script, link, link, script, input#_w_brink, body, a, div#home, div#header, div#blogTitle, a#lnkBlogLogo, img#blogLogo, h2, a#Header1_HeaderTitle.headermaintitle.HeaderMainTitle, h3, div#navigator, ul#navList, li, a#blog_nav_sitehome.menu, li, a#blog_nav_myhome.menu, li, a#blog_nav_newpost.menu, li, a#blog_nav_contact.menu, li, a#blog_nav_rss.menu, li, a#blog_nav_admin.menu, div.blogStats, span#stats_post_count, span#stats_article_count, span#stats-comment_count, div#main, div#mainContent, div.forFlow, div#post_detail, div#topics, div.post, h2.postTitle, a#cb_post_title_url.postTitle2.vertical-middle, span, div.clear, div.postBody, div#cnblogs_post_body.blogpost-body, p, p, strong, p, p, p, strong, div.cnblogs_code, pre, span, span, span, span, span, p, span, strong, pre, strong, span, strong, br, br, br, div.cnblogs_code, pre, span, span, p, p, …]
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__proto__: NodeList

使用 document.querySelectorAll 实现如下

const maxBy = (list, keyBy) => list.reduce((x, y) => keyBy(x) > keyBy(y) ? x : y)

function getFrequentTag () {
  const tags = [...document.querySelectorAll('*')].map(x => x.tagName).reduce((o, tag) => { 
    o[tag] = o[tag] ? o[tag] + 1 : 1;
    return o
  }, {})
  return maxBy(Object.entries(tags), tag => tag[1])
}

使用 element.children 递归迭代如下 (最终结果多一个 document)

function getAllTags(el = document) {
  const children = Array.from(el.children).reduce((x, y) => [...x, ...getAllTags(y)], [])
  return children
}

// 或者通过 flatMap 实现
function getAllTags(el = document) {
  const children = Array.prototype.flatMap.call(el.children, x => getAllTags(x))
  return [el, ...children]
}