I get wrong coordinates when converting shapefiles with "EPSG:2100" - GGRS87 / Greek Grid - Projection

[Userrrfriendly]

Hello, I am trying to convert shapefiles with "EPSG:2100" projection (the official coordinate system for Greece). Shapefile-js by default tries to convert them to good old "EPSG:4326" - WGS84, but unfortunately the transformed coordinates that I get in the geoJSON file are quite off (~300m offset). Does anyone know if there is a workaround for my case?
The best case would be that the transformation worked on the fly, if that's not possible I'm fine if the coordinates stayed in the original projection so I could re-project them manually.

I have attached some sample data in both systems.
TestingPoints_.zip