The ESP32 has an internal magnetic field sensor. Just google for "esp32 hall sensor", and you can find more details. In the arduino library it's a single call, so shouldn't be too hard to port the code...
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.
what's the Hall Sensor? is it called something else?