Implementing controls using the Gamepad API - Game development
mapping standard the mapping type is now an enumerable object instead of a string: enum gamepadmappingtype { "", "standard" }; this enum defines the set of known mappings for a gamepad.

Inputs and input sources - Web APIs
the most notable—but not the only—difference is that webxr adds the xr-standard gamepad mapping, expanding the gamepadmappingtype enumerated type.