取得浏览器的文档类型

      var DOCTYPE = "",doctype;
      if((doctype = document.doctype)) {
        DOCTYPE += '<!DOCTYPE ' + doctype.name +(doctype.publicId ? (' '+doctype.publicId+ ' "' + doctype.systemId + '">')  :'>')
      }else if((doctype = document.getElementsByTagName("!")[0])){
        DOCTYPE = doctype.text;
      }
      alert(DOCTYPE);

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原文地址：https://www.cnblogs.com/rubylouvre/p/2039605.html