How can I make an OBJ + MTL loaded doublesided?

with the loader bellow the obj and mtl files are loaded, so how can I access the material and make it doublesided?
If I use mtlLoader.setMaterialOptions(side: THREE.DoubleSide) as in the following documentation page, it doesn’t work -and I’m not getting any hinting from VScode about the .setMaterialOptions either.

Here’s the main part of the obj+mtl loader:

			var mtlLoader = new THREE.MTLLoader();
			mtlLoader.setPath( 'female02/' );
			mtlLoader.load( 'female02.mtl', function( materials ) {					

				var objLoader = new THREE.OBJLoader();
				objLoader.setMaterials( materials );
				objLoader.setPath( 'female02/' );
				objLoader.load( 'female02.obj', function ( object ) {
					object.position.set( 0, -95, 0 );					
					sceneRTT.add( object );
				}, onProgress, onError );


Solution: curly braces were needed -that should have been mentioned on the documentation:
mtlLoader.setMaterialOptions({side: THREE.DoubleSide}) ;