three.js how to make double sided object

In your case, you add the following to your callback function:

objects.traverse( function( node ) {
    if( node.material ) {
        node.material.side = THREE.DoubleSide;
    }
});

The doubleSided property of Mesh is deprecated. It was replaced with the side property of Material

Also, it is best to learn from three.js examples that work with the current version of the library.

three.js r.57