How to use the @iiif/vocabulary.MediaType.THREEJS function in @iiif/vocabulary

load: this._extensions[Extension.PDF]
        };

        this._extensionRegistry[MediaType.AUDIO_MP4] = {
            load: this._extensions[Extension.AV]
        };

        this._extensionRegistry[MediaType.VIDEO_MP4] = {
            load: this._extensions[Extension.AV]
        };

        this._extensionRegistry[MediaType.WEBM] = {
            load: this._extensions[Extension.AV]
        };

        this._extensionRegistry[MediaType.THREEJS] = {
            load: this._extensions[Extension.VIRTEX]
        };

        this._extensionRegistry[MediaType.MP3] = {
            load: this._extensions[Extension.AV]
        };

        this._extensionRegistry[MediaType.M3U8] = {
            load: this._extensions[Extension.AV]
        };

        this._extensionRegistry[MediaType.MPEG_DASH] = {
            load: this._extensions[Extension.AV]
        };

        this._extensionRegistry["av"] = {