How can i load a fbx file with attribute 'index'?

I’m trying to load the model and do cloth simulation on it. But I find that the loaded model(fbx file) has no attribute index(using FBXLoader). And I need the ‘index’ to do cloth simulation.

Moreover I find that all the loaders integrate the ‘position’ and the ‘index’ attributes in original file into one called ‘position’ when loading and just use ‘position’ to render the model.
So i wonder if there is any way to load model and reserve the attribute ‘index’ or there is any way to compute the ‘index’ on the loaded model. Thanks.

Index should be an attribute of the geometry, any chance you can share the model or a live example with the loaded model here? Using BufferGeometryUtils.mergeVertices should generate an index for the geometry in question but this may be unnecessary on inspection of the model / code you’re using…