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

Syntax

mode = document.compatMode;

Values

mode
Is an enumerated value that can be:
  • "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 defined in standards, so the older "standards" and "almost standards" names are nonsensical and no longer used in standards.

Example

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

Specifications

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
Basic support
Non-standard
Chrome Full support YesEdge ? Firefox Full support YesIE ? Opera ? Safari ? WebView Android Full support YesChrome Android Full support YesEdge Mobile ? Firefox Android Full support YesOpera Android ? Safari iOS ? Samsung Internet Android ?

Legend

Full support  
Full support
Compatibility unknown  
Compatibility unknown
Non-standard. Expect poor cross-browser support.
Non-standard. Expect poor cross-browser support.

Document Tags and Contributors

Last updated by: mfluehr,