Ah, just for anybody blind as I am - the "watch and upload" function is to be found in the online version of the IDE at https://www.espruino.com/ide/ and seems unavailable in the Chrome webapp.
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.
Ah, just for anybody blind as I am - the "watch and upload" function is to be found in the online version of the IDE at https://www.espruino.com/ide/ and seems unavailable in the Chrome webapp.