This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.
In other words, the current acceleration of the sensor, along the
var myGamepadLinAcc = gamepadPoseInstance.linearAcceleration;
null if the gamepad is not able to provide linear acceleration data.
The definition of 'linearAcceleration' in that specification.