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Editorial Team
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Asked: 2026-06-08T08:47:32+00:00

So let’s say (in IE8) that we have a document . Now normally we

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So let’s say (in IE8) that we have a document.

Now normally we can assume that document.childNodes[0] is the doctype. So

var doctype = document.childNodes[0]

Now how do we confirm rather then assume it is the doctype?

doctype.nodeType === Node.COMMENT_NODE;
doctype.tagName === "!"; // same as a comment
doctype.data.indexOf("DOCTYPE ") > -1; // same as any comment containing the word DOCTYPE.
doctype === document.doctype; // false, document.doctype is undefined in IE8

Apart from assumptions, how am I supposed to know whether a given node is a doctype?

For those of you unfamiliar with DOM4 take a look at DocumentType

The DOM-shim get’s document.doctype in IE8 by just returning document.childNodes[0]

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1 Answer

  1. Editorial Team

    I figured out that in IE7 and IE8 the .innerHTML property for comments is always the full "<!--comment here-->" and for the doctype node, it is "". Even for empty comments, the .innerHTML is "<!---->"

    So based on this I created:

    function isDocType(node) {
    return node && (
    node.nodeType === 10 || (node.nodeType === 8 && "innerHTML" in node && node.innerHTML === ""));
}

    With the test page:

    <!-- comment1 -->
<!-- comment2 -->
<!---->
<!-- -->
<!-- <!DOCTYPE html> -->

    Running doctype and the comments through isDocType gives:

    LOG: true 
LOG: false 
LOG: false 
LOG: false 
LOG: false 
LOG: false

    See http://jsfiddle.net/AEYt4/

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