2018.3 Getting trigger state (for example)

How would you get the state of (for example) a VR trigger in Unity 2018.3?

In 2019.1 there is InputDevice.TryGetFeatureValue (with a broken help page):
https://docs.unity3d.com/2019.1/Documentation/ScriptReference/XR.InputDevice.html

In 2018.3 it does not exist:
https://docs.unity3d.com/2018.3/Documentation/ScriptReference/XR.InputDevice.html

I've also looked at XRNodeState, InputDevices and InputTracking, but I don't see anything.