THREE.JSONLoader was removed with the latest release R99. Hence, it’s not possible to use THREE.ObjectLoader in order to load geometry data of type THREE.Geoemtry anymore.
There is a fallback solution. If you include the following file, it should be possible to use THREE.ObjectLoader as before:
However, you should not use the Blender JSON exporter anymore. It’s very important that you switch to better solutions. three.js recommends to use the glTF 3D format. There are glTF exporters for Blender and a respective GLTFLoader. More information right here:
https://threejs.org/docs/index.html#manual/en/introduction/Loading-3D-models