Get DocType of an HTML as string with Javascript

Question

I know that I can access to doctype object via document.doctype or document.childNodes[0] but my problem is getting doctype as a string. I can do this in chrome and safari by calling document.doctype which returns <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">. However in Firefox, calling document.doctype returns DocumentType object.

Is there a way to get the doctype string in all browsers as in chrome and safari?

Thanks!

Christoph · Accepted Answer · 2012-12-04 09:07:58Z

82

In all compliant browsers (including Chrome/Safari), document.doctype also returns a DocumentType object. The following code can be used to generate a valid DOCTYPE string.

var node = document.doctype;
var html = "<!DOCTYPE "
         + node.name
         + (node.publicId ? ' PUBLIC "' + node.publicId + '"' : '')
         + (!node.publicId && node.systemId ? ' SYSTEM' : '') 
         + (node.systemId ? ' "' + node.systemId + '"' : '')
         + '>';

This method returns the correct string for valid (HTML5) doctypes, eg:

<!DOCTYPE html>
<!DOCTYPE html SYSTEM "about:legacy-compat">
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN" "http://www.w3.org/TR/REC-html40/strict.dtd">

Explanation of the code:

node.name      # Holds the name of the root element, eg: HTML / html
node.publicId  # If this property is present, then it's a public document type.
               #>Prefix PUBLIC
!node.publicId && node.systemId
               # If there's no publicId, but a systemId, prefix SYSTEM
node.systemId  # Append this if present

edited Dec 4, 2012 at 9:07

Christoph

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answered Apr 15, 2012 at 13:14

Rob W

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1 Comment

Brad Koch Over a year ago

Worth noting documents with no DOCTYPE have a document.doctype === null.

Pavlo · Accepted Answer · 2015-01-29 13:29:23Z

58

You can also use this one liner to get the current doctype. This will work in any modern browser and IE 9 and higher.

new XMLSerializer().serializeToString(document.doctype);

edited Jan 29, 2015 at 13:29

Pavlo

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answered Jan 8, 2015 at 11:22

Scott

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1 Comment

vee Over a year ago

This will be added xmlns attribute.

codeassembly · Accepted Answer · 2012-05-02 07:36:12Z

3

function get_doctype()
{
    var doctype = 
    '<!DOCTYPE ' + 
    document.doctype.name +
    (document.doctype.publicId?' PUBLIC "' +  document.doctype.publicId + '"':'') +
    (document.doctype.systemId?' "' + document.doctype.systemId + '"':'') + '>';
    return doctype;
}

answered May 2, 2012 at 7:36

codeassembly

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Comments

T1000 · Accepted Answer · 2011-05-22 15:46:07Z

1

Is that what are you looking for ?

alert(document.doctype.publicId);

answered May 22, 2011 at 15:46

T1000

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2 Comments

matte Over a year ago

That returns only -//W3C//DTD HTML 4.01//EN. I need whole DOCTYPE

T1000 Over a year ago

Maybe you need to do --- var doc = '<!DOCTYPE '+document.doctype.name+' PUBLIC "'+document.doctype.publicId+'" "'+document.doctype.systemId+'">';

KooiInc · Accepted Answer · 2011-05-22 15:53:32Z

1

Concatenate DocumentType.name, .publicId and .systemId. Something like:

'<!DOCTYPE '+ 
  DocumentType.name+' PUBLIC "'+ //maybe you should check for publicId first
  DocumentType.publicId+'" "'+
  DocumentType.systemId+'">'

answered May 22, 2011 at 15:53

KooiInc

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3 Comments

Kendall Hopkins Over a year ago

I'm guessing this doesn't support HTML5?

KooiInc Over a year ago

@Kendall: it does, but isn't very informative for html5 afaik.

Kendall Hopkins Over a year ago

I mean, it should print <!DOCTYPE html>, but for this page (which uses HTML5 doctype), I get <!DOCTYPE html PUBLIC "" "">.

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