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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@Gordon
It was a Pico and the exact reader you see here: http://www.espruino.com/MFRC522
The cards used to read/write were the cards that you get given with the reader - the type of card you use definitely matters as they can use different protocols.
The code itself was mostly based on https://github.com/pimylifeup/MFRC522-python so you could try connecting to a Raspberry Pi and using the Python code to see if that works