Document: compatMode property

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The Document.compatMode read-only property indicates whether the document is rendered in Quirks mode or Standards mode.

Value

A string that is one of the following:

  • "BackCompat" if the document is in quirks mode.
  • "CSS1Compat" if the document is in no-quirks (also known as "standards") mode or limited-quirks (also known as "almost standards") mode.

Note: All these modes are now standardized, so the older "standards" and "almost standards" names are nonsensical and no longer used in standards.

Examples

js
if (document.compatMode === "BackCompat") {
  // in Quirks mode
}

Specifications

Specification
DOM
# ref-for-dom-document-compatmode①

Browser compatibility

Report problems with this compatibility data on GitHub
desktopmobile
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
compatMode

Legend

Tip: you can click/tap on a cell for more information.

Full support
Full support
Partial support
Partial support
Has more compatibility info.