Wifi.connect() not executing its callback function

Give this a try:

//ESP32wifi.js
// 5 Feb2018

var ssid="ssid";
var key="keykey";
console.log('start');

var wifi = require('Wifi'); 
wifi.connect(ssid, {password: key}, 
function onWiFiConnect(){
  console.log("xxx");
 
  var IPobject = wifi.getIP();
 
  var IP = IPobject.ip;
  var MAC = IPobject.mac;
 
  console.log("IP:");
  console.log(IP);
 
  console.log("MAC:");
  console.log(MAC);
});
 

Which produces:

 1v95 Copyright 2017 G.Williams
Espruino is Open Source. Our work is supported
only by sales of official boards and donations:
http://espruino.com/Donate
>start
=undefined
xxx
IP:
192.168.1.14
MAC:
24:0a:c4:00:97:2a
> 

At first your code wouldn't load and would complain the module wifi was not found.
The cure was to exit WebIDE and uplug then start over.