Mujoco_WASM/test/user/testdata/cube_with_mesh_def.xml

<mujoco>
  <default>
    <default class="mesh">
      <mesh scale="2 2 2"/>
    </default>
  </default>

  <asset>
    <mesh file="cube.obj" class="mesh"/>
  </asset>

  <worldbody>
    <geom type="mesh" mesh="cube"/>
  </worldbody>
</mujoco>