This is a Deno library that is largely a port of the Ruby fitreader library. It is capable of parsing and decoding .FIT files, which are a binary data format used by GPS devices and various sensors. It should be noted, it has only been tested and proven to support my Garmin Venu .FIT files and a few .FTI files that I found in other repositories. YMMV.
It has a very small API footprint, exposing a single class which is capable of handling all of the processing.
See mod.ts.