You may be right.. Not sure. But I see the green LED looks very weak. (see video) Would be nice if there was some way to determine the battery voltage externally. Hey ho.
Edit: won't let me upload the video. Here is a link to it instead.
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.
Check the battery voltage or swap with a fresh battery...