systemId (W3C DOM Core property)

Version Depr. Static Read-only
DOM2 No No Yes
Browser support (more…)
IE5.5+ FF1.5+ SA3+ OP9+
Partial Full Full Full


var sysid = document.doctype.systemId;

The example above saves a reference to the systemId of the doctype. So if we were on a page with an XHTML 1.0 Strict doctype, the sysid variable would have the value


The system identifier of an Entity or Notation, and in DOM 2 of a DocumentType, or null if no system identifier is specified.

This property is readonly.


Internet Explorer Firefox Safari Opera
5.5 6.0 7.0 1.5 2.0 3.0 1.3 2.0 3.0 9.0 9.5
Partial Partial Partial Full Full Full None None Full Full Full

Only Opera, Firefox and Safari 3 are able to retrieve the systemId of a DocumentType. In Internet Explorer in XML the property is undefined; in Safari 1.3 and 2 in XHTML mode or XML1 it's null; otherwise the doctype property itself is null.

Only Opera in XHTML mode or XML and Internet Explorer in XML are able to retrieve the systemId of an Entity or Notation, because those are the only environments in which the root objects themselves are exposed (see Entity and Notation for details).


1 On XHTML pages served as application/xhtml+xml.

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