这是是标准行为,实际是挂载在 window 上面的。你在你的业务代码里面也可以这样使用,但是不建议。
见标准:"HTML
Standard" (https://link.segmentfault.com/?enc=ssW48WCWiFRiyj45h%2B%2BCZg%3D%3D.yjwF%2B10giujgQbKIuXXP5Ex4fcDvJJ8RRBwk3CtIQSy5yq7KVia9VCbBSg%2BP5TXk%2FGVjlUTWlTbKSYmtUrCDiQ%3D%3D)
见相关文章:"搜索:getElement*,querySelector*" (https://link.segmentfault.com/?enc=dmMdYkxPXv02%2F44XHSt%2FWQ%3D%3D.vSfhunLACCNa3%2BoGNMwtbvnUnye0u18gU80%2FkmmYSTadgGxr9URHVtErXmxPY4sLjg27AwXFovJc8vtXttB6Ns1brg4csNzd7xOR9k7Gg2vi%2Bv0wOay1%2BPF0AJB%2Brm%2BhIbfKT4RZxbPdnoyqhxgFAw%3D%3D)