Enable smooth shading with Three.js

Question

I'm rendering an object with textures using MTL and OBJ files with Three.js. My code here works but my model is displayed as flat shaded. How do I enable smooth shading?

var scene = new THREE.Scene();  
var mtlLoader = new THREE.MTLLoader();
mtlLoader.setPath('assets/');
mtlLoader.setBaseUrl('assets/');
mtlLoader.load('asset.mtl', function(materials) {

    materials.preload();

    var objLoader = new THREE.OBJLoader();
    objLoader.setMaterials(materials);
    objLoader.setPath('assets/');
    objLoader.load('asset.obj', function(object) {

       //
       // This solved my problem
       //
       object.traverse(function(child) {
           if(child instanceof THREE.Mesh)
           {
              child.material.shading = THREE.SmoothShading;
           }
       });
       //
       //

       scene.add(object);
    });
});

EDIT: I updated my code with a solution that fixed my problem based on the accepted answer.

Answer 1

It could be one of two things that I can think of right now.

It could be that the material is set to FlatShading. In this case just somehow retrieve the object and use object.material.shading = THREE.SmoothShading; to fix.

If that doesn't change it, it's possible that the object contains per-vertex-normals (meaning that every vertex of every triangle has a normal attached to it) and that all normals for each triangle point in the same direction. This is something that should better be solved in the 3d-editing process, but you can also re-compute the normals in three.js:

object.geometry.computeVertexNormals(true);

This should [1] recompute the normals for smooth surfaces. However, it will only work for regular Geometries and Indexed BufferGeometries (or, to put it the other way around: it won't work if the geometry doesn't have information about vertices being reused for adjacent faces)

[1]: I didn't test it myself and just go after what I just read in the code