There are a few things you might want to know if you’re looking to change the document type (doctype) using jQuery or Javascript. First, doctype is listed as a property in the W3C documentation, and is defined as read-only:
interface Document : Node {
readonly attribute DocumentType doctype;
readonly attribute DOMImplementation implementation;
readonly attribute Element documentElement;
Element createElement(in DOMString tagName)
raises(DOMException);
DocumentFragment createDocumentFragment();
While it may be possible to insert a doctype with javascript / jquery above the HTML tag, it is not advisable to do so. Sample code which would do this might look like:
<!-- no doctype, loads in Quirks Mode (BackCompat) -->
<html>
<!-- rest of the document, then at the end: -->
<script>
alert('now in compatMode '+document.compatMode);
if (document.compatMode==='BackCompat') {
setTimeout(function() {
var markup= document.documentElement.innerHTML;
markup= '< !DOCTYPE html><html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">'+markup+'</html>';
document.open();
document.write(markup);
document.close();
}, 0);
}
</script>
</html>
