easiest may be using the https://www.nordicsemi.com/Products/Development-software/nrf5-sdk-for-thread-and-zigbee which is based on nrf5 sdk 16 so building espruino with it may not be hard see also https://infocenter.nordicsemi.com/index.jsp?topic=%2Fstruct_sdk%2Fstruct%2Fsdk_thread_zigbee_latest.html
Another option is nRF Connect SDK which is based on Zephyr - very different to older Nordic SDK https://www.nordicsemi.com/products/zigbee
@fanoush started
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.
easiest may be using the https://www.nordicsemi.com/Products/Development-software/nrf5-sdk-for-thread-and-zigbee which is based on nrf5 sdk 16 so building espruino with it may not be hard see also https://infocenter.nordicsemi.com/index.jsp?topic=%2Fstruct_sdk%2Fstruct%2Fsdk_thread_zigbee_latest.html
Another option is nRF Connect SDK which is based on Zephyr - very different to older Nordic SDK
https://www.nordicsemi.com/products/zigbee