yes, that's in uniform upload. These are usually in the hottest place of the rendering loop so I'm trying to choose the best strategy. In JS non-typed arrays are faster than typed(at least in V8)). Given an object with some properties i.e. position(vec3) and matrix (mat4x4) that are being pushed as uniforms, which will be the best choice:
A) Always operate on typed arrays that will be pushed to uniforms - slower operations in JS (read/write, multiplying matrices etc)
B) Operate on non-typed arrays and copy to temp typed just before pushing uniforms - cost of copying on each uniform upload before every drawcall
C) Only operate on non-typed arrays and directly push them as uniforms - hidden conversion cost(if there is any) about which I'd like to know more