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
}