Architecture: WiFi support for WiFi enabled boards ...

How do I teach the IDE that Wifi is a built-in module?

It'll 'just happen' next time I update the website with a new release (it gets listed in the json/ESP8266_BOARD.json file on espruino.com).

wrt callback parameters: It's a pretty standard JS/NodeJS thing to have:

function (err, data) {
  if (err) {
    console.log("Oh no!");
    return;
  }
  // ...
}

It's not pretty, but it's what everyone does. It'd be nice to be able to keep that kind of thing wherever possible.