For anyone interested in embedded JavaScript but wants broader hardware support and/or modern JavaScript support[1], the XS JavaScript engine is microcontroller-independent[2], and Moddable provides supported ports for ESP8266, ESP32 (the successor to ESP8266), and the Gecko series of processors. (They also sell some hardware kits for folks who want that: https://www.moddable.com/product.php)

[1] Espruino supports ES5, XS supports ECMAScript 2018 [2] https://www.moddable.com/faq.php#microcontrollers