[nulagrithom]

If you Google '204 EDI specification' you should find a lot of random specs in PDF out there for various companies. 214 will show you some of the status updates too. Stuff like this: http://www.shipfsp.com/media/pdf/it/EDI_214_X12_V4010.pdf

I've found this EDI notepad useful for parsing flat files: https://www.liaison.com/products/integrate/edi-notepad/

And this npm library actually parses EDIs pretty well too: https://www.npmjs.com/package/x12