Document.doctype is a read-only instance property that returns a DocumentType object for the document’s Document Type Declaration (DTD), or null if none exists. Learn name, publicId, systemId, how HTML5 doctypes look, and five examples with try-it labs.
Read-only
DocumentType
null
name "html"
Not via DOM
Baseline widely
At the top of almost every HTML file you write <!DOCTYPE html>. That line is the document type declaration. It tells the browser which kind of document rules to use (and historically avoided quirks mode).
MDN: document.doctype is the read-only DocumentType object for that declaration. If the document has no DTD, the property is null. You cannot edit the doctype through the DOM (DOM Level 2 does not support editing it).
For <!DOCTYPE html>, expect doctype.name === "html" with empty publicId and systemId. Older XHTML/HTML4 doctypes carried longer public/system identifiers.
Related Document tutorials: dir, compatMode, Document constructor.
Document.doctypeA read-only instance property on Document. Value is a DocumentType node or null.
name — root type name (e.g. "html").publicId — public identifier string (often empty in HTML5).systemId — system identifier string (often empty in HTML5).internalSubset — internal DTD subset string when present (MDN example).document.doctype.document.doctypeA DocumentType object, or null if there is no DTD (MDN).
const doctypeObj = document.doctype;
console.log(`doctypeObj.name: ${doctypeObj.name}`);
console.log(`doctypeObj.internalSubset: ${doctypeObj.internalSubset}`);
console.log(`doctypeObj.publicId: ${doctypeObj.publicId}`);
console.log(`doctypeObj.systemId: ${doctypeObj.systemId}`);| Goal | Code / note |
|---|---|
| Get DocumentType | document.doctype |
| Safe name | document.doctype?.name |
| HTML5 check | document.doctype?.name === "html" |
| Missing doctype | document.doctype === null |
| Standards mode | document.compatMode === "CSS1Compat" |
| MDN status | Baseline Widely available |
Four facts about document.doctype.
DocumentType | nullOr null
read-onlyNo setter
name: "html"Typical
baselineStandard API
| Property | Meaning | HTML5 example |
|---|---|---|
name | Declared root name | "html" |
publicId | Formal public identifier | "" |
systemId | System identifier / URI | "" |
internalSubset | Internal subset string | Usually empty / unused in HTML5 |
Examples follow MDN Document: doctype. Use View Output or Try It Yourself for each case.
Read the DocumentType and log its fields (MDN).
document.doctypeConfirm the page has a doctype node.
console.log(document.doctype);
// DocumentType { name: "html", ... } on a normal HTML5 pageThe browser exposes the parsed doctype as a node at the start of the document tree.
MDN’s example logging the main DocumentType fields.
const doctypeObj = document.doctype;
console.log(`doctypeObj.name: ${doctypeObj.name}`);
console.log(`doctypeObj.internalSubset: ${doctypeObj.internalSubset}`);
console.log(`doctypeObj.publicId: ${doctypeObj.publicId}`);
console.log(`doctypeObj.systemId: ${doctypeObj.systemId}`);Guard with if (document.doctype) before reading fields if the document might lack a DTD.
Practical diagnostics for modern pages.
Name is html with empty public/system ids.
const dt = document.doctype;
const isHtml5Like =
!!dt &&
dt.name.toLowerCase() === "html" &&
!dt.publicId &&
!dt.systemId;
console.log("HTML5-like doctype:", isHtml5Like);This heuristic matches common HTML5 pages; XML/SVG documents may differ.
Created documents may not expose a doctype.
const fresh = document.implementation.createHTMLDocument("Scratch");
console.log("Main has doctype:", document.doctype !== null);
console.log("Fresh doctype:", fresh.doctype);
console.log("Fresh name:", fresh.doctype?.name ?? "(none)");MDN: the property returns null when no DTD is associated. Always optional-chain in shared helpers. (createHTMLDocument often includes an HTML doctype in modern browsers.)
compatModeDoctype presence and rendering mode are related diagnostics.
const info = {
hasDoctype: document.doctype !== null,
name: document.doctype?.name ?? null,
compatMode: document.compatMode
};
console.log(JSON.stringify(info, null, 2));See also compatMode for quirks vs standards rendering.
name / ids beside compatMode.<!DOCTYPE html> becomes in the DOM.CSS1Compat mode.<!DOCTYPE html> (or a longer legacy DTD).
Creates a node with name / publicId / systemId.
Available as document.doctype.
Inspect for diagnostics; fix markup at the source if needed.
DocumentType or null..name and related fields.Document.doctype is marked Baseline Widely available on MDN (since July 2015). Logos use the shared browser-image-sprite.png sprite from this project.
Read-only DocumentType for the document's DTD — or null if none is associated.
Bottom line: Use document.doctype to inspect the DocumentType. Always include in HTML source — you cannot set the doctype from JavaScript.
Document.doctype exposes the parsed Document Type Declaration as a DocumentType node. On modern HTML5 pages that usually means name: "html". Read it for diagnostics; fix doctypes in your HTML source, not with a JavaScript assignment.
Continue with documentElement, compatMode, dir, or the JavaScript hub.
<!DOCTYPE html>document.doctype before reading fieldscompatMode in support reportsdoctype?.name)document.doctypecontentType (MIME)document.doctypeRead-only DocumentType — or null when missing.
DocumentType
APIbaseline
Standardread-only
DOMnull
MDNname html
TypicalBefore HTML5’s short <!DOCTYPE html>, authors copied long SGML-style doctypes with public and system identifiers. Those still appear as non-empty publicId / systemId on document.doctype when you open old pages.
Learn how to access the document’s root Element (usually <html>).
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