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document.compatMode

Indicates whether the document is rendered in Quirks mode or Standards mode.

Syntax

mode = document.compatMode

Values

  • "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.
mode
Is an enumerated value that can be:

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

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https://developer.mozilla.org/en-US/docs/Web/API/document/compatMode