Yes I have written a couple of programs for the esp device, and used spiffs to hold a webpage, its cool.
I was interested in this as the general concept is that the microcontroller itself runs the javascript rather than the usual C or assembler, I liked the idea of that.
J5 dies say that the 'duino doesnt actually run the code, the browser does and controls the 'duino's i/o, and kinda makes it appear like the 'duino is running the script.
Being able to do this via the web with an esp would be cool, the more I look at it though it does look like the code running on the 'duino is meant for the At328 not the esp.