Cannot connect to ESP8266

If you can connect and upload over Wifi that's good. Odd that you have problems over serial. I haven't experienced it that way round.

wifi.save() is for setting up your wifi connection and storing so the board will join your network (or say act as an AP) when booted. For saving other programs it's save(). It won't be stored unless you save it.

Check out E.on("init",...) if you want that code to run when your board is restarted.

You should also check out this page http://www.espruino.com/Quick+Start

One final thing. If you're new to Espruino, you'll make better progress if you get a Pico or original Espruino. It will work out the box - and speed you up the curve. Plus you can test code on there before you move it to ESP8266.