Accessing Doctype with Javascript

htmlVersion.js

var Doctype;
var publicId;
var search;
var htmlVersion;
 
if (document.doctype) {
  publicId = document.doctype.publicId;  
} else { 
  /* document.doctype doesn't exist - detect Explorer */
  var IE = /*@cc_on!@*/false;
 
  if (IE) {  
    if (document.all[0].nodeType == 8) {
      Doctype = document.all[0].nodeValue;
      search = Doctype.match(/^DOCTYPE\s+(html|math|svg)\s+(SYSTEM|PUBLIC)\s+"(.*\/\/EN)".*$/i);
    }
    if (search[3]) publicId = search[3]; 
  }
 
}
 
if (publicId != null) { 
  if (publicId !== '') { 
    search = publicId.match(/^\-\/\/W3C\/\/DTD(.*)\/\/EN$/i);
    htmlVersion = (search[1] != null) ? search[1] : 'Unknown'; 
  } else {
    htmlVersion = 'HTML 5';
  }
} else { 
  htmlVersion = 'Unknown';
}
 
alert (htmlVersion);