That would be dependant on many factors. Brain.js say in the README that this library is not ideal for millions of points. I believe this is due to the speed complexities of it being interpreted rather than compiled.
In my experience, this framework performs well with a few hundred / low thousand floating point values, but there is a big speed knock off with anything higher.
There is another library called Synaptic which may handle larger networks better. If there is enough interest I will make another tutorial using this library and more floating points to test performance.