code: function ( textureMap, id ) {
  
  			// if the texture is a layered texture, just use the first layer and issue a warning
  			if ( 'LayeredTexture' in fbxTree.Objects && id in fbxTree.Objects.LayeredTexture ) {
  
  				console.warn( 'THREE.FBXLoader: layered textures are not supported in three.js. Discarding all but first layer.' );
  				id = connections.get( id ).children[ 0 ].ID;
  
  			}
  
  			return textureMap.get( id );
  
  		}
docs: get a texture from the textureMap for use by a material.