How to include OVRManager in Three.js Scene?

I have created several Three.js/Javascript demo applications that I'm experimenting with in my new Oculus Go. I'm trying to enable the Go Controller to do stuff in my applications, and according to the Oculus Developer Center, the best thing to do is to include OVRManager in my scene so I have access to that API. That sounds good, but for all the documentation (https://developer.oculus.com/documentation/unity/latest/concepts/unity-ovrinput/) I can't see HOW to add OVRManager to my scene! I have not worked with Unity before, but from what I can tell in the documentation there shouldn't be any compatibility issues (should there?)

So what I'd think to do is something like:

<script src="OVRManager.js or something like that"></script>

and then call the functions I need, as I've done with OrbitControls.js and other external dependencies.

But for the life of me, Google searching is just sending me in circles. I see questions posed for C++ and C# but that's of no use to me. How do I get this API working in my Three.js scene? Where do I find it and is there some other way to include it?

Thanks!

Create a unity WebGL build and expose the API you need as public methods in a Unity Script you attach to a GameObject.

Then, you should be able to follow the directions at How to call Unity functions from javascript (copied below) on how to call those methods from your javascript code.

You may be able to use UnityScript, which is vaguely similar to JavaScript, to write the Script if you use an old version of Unity. As of this writing, Oculus recommends version 2017.4.11f1, which I think might still support UnityScript.

One major reason you see so much less UnityScript information is that Unity has been moving away from UnityScript, into only supporting C#.

But regardless of if you code your OVRManager script in C# or UnityScript, Unity will make the methods callable from your JavaScript.

Calling Unity scripts functions from JavaScript

Sometimes you need to send some data or notification to the Unity script from the browser’s JavaScript. The recommended way of doing it is to call methods on GameObjects in your content. If you are making the call from a JavaScript plugin, embedded in your project, you can use the following code:
SendMessage(objectName, methodName, value);
Where objectName is the name of an object in your scene; methodName is the name of a method in the script, currently attached to that object; value can be a string, a number, or can be empty. For example:
SendMessage('MyGameObject', 'MyFunction');
SendMessage('MyGameObject', 'MyFunction', 5);

SendMessage('MyGameObject', 'MyFunction', 'MyString');
If you would like to make a call from the global scope of the embedding page, see the Code Visibility section below.

Code visibility

Starting from Unity 5.6 all the build code is executed in its own scope. This approach makes it possible to embed your game on an arbitrary page without causing conflicts with the embedding page code, as well as makes it possible to embed more than one build on the same page.

If you have all your JavaScript code in the form of .jslib plugins inside your project, then this JavaScript code will run inside the same scope as the compiled build and your code should work pretty much the same way as in previous versions of Unity (for example, the following objects and functions should be directly visible from the JavaScript plugin code: Module, SendMessage, HEAP8, ccall etc.).

However, if you are planning to call the internal JavaScript functions from the global scope of the embedding page, you should always assume that there are multiple builds embedded on the page, so you should explicitly specify which build you are referencing to. For example, if your game has been instantiated as:
var gameInstance = UnityLoader.instantiate("gameContainer", "Build/build.json", {onProgress: UnityProgress});
Then you can send a message to the build using gameInstance.SendMessage(), or access the build Module object using gameInstance.Module.