add( object ) {

		if ( arguments.length > 1 ) {

			for ( let i = 0; i < arguments.length; i ++ ) {

				this.add( arguments[ i ] );

			}

			return this;

		}

		if ( object === this ) {

			console.error( 'THREE.Object3D.add: object can\'t be added as a child of itself.', object );
			return this;

		}

		if ( object && object.isObject3D ) {

			object.removeFromParent();
			object.parent = this;
			this.children.push( object );

			object.dispatchEvent( _addedEvent );

			_childaddedEvent.child = object;
			this.dispatchEvent( _childaddedEvent );
			_childaddedEvent.child = null;

		} else {

			console.error( 'THREE.Object3D.add: object not an instance of THREE.Object3D.', object );

		}

		return this;

	}
Adds the given 3D object as a child to this 3D object. An arbitrary number of
objects may be added. Any current parent on an object passed in here will be
removed, since an object can have at most one parent.

@fires Object3D#added
@fires Object3D#childadded
@param {Object3D} object - The 3D object to add.
@return {Object3D} A reference to this instance.