The MediaTrackSettings dictionary's height property is an integer indicating the number of pixels tall MediaStreamTrack is currently configured to be. This lets you determine what value was selected to comply with your specified constraints for this property's value as described in the MediaTrackConstraints.height property you provided when calling either getUserMedia() or MediaStreamTrack.applyConstraints().
If needed, you can determine whether or not this constraint is supported by checking the value of MediaTrackSupportedConstraints.height as returned by a call to MediaDevices.getSupportedConstraints(). However, typically this is unnecessary since browsers will ignore any constraints they're unfamiliar with.