Get WhatsApp Web Group Phone Number (last update 10 Sep 2017), Tested on Google Chrome Developer Console

wa-group-phone-number.js

var obj = document.getElementsByClassName("infinite-list-viewport")[0].getElementsByClassName("infinite-list-item infinite-list-item-transition");
console.log("Group Name : " + document.getElementsByClassName("input-wrapper locked")[0].getElementsByTagName("div")[1].innerHTML);
console.log("Number of participants : " + obj.length);
var iObj;
for(var i=0;i<obj.length;i++){
var nama = obj[i].getElementsByTagName("div")[0].getElementsByTagName("span")[3].getElementsByTagName("span")[0];
var nama2 = obj[i].getElementsByTagName("div")[0].getElementsByTagName("span")[2].getElementsByTagName("span")[0];
var nope = obj[i].getElementsByTagName("div")[0].getElementsByTagName("span")[1].title;
if(nama != undefined) {
  console.log(nama.innerText + "\t" + nope);	
} else if(nama2 != undefined) { 
  console.log(nama2.innerText + "\t" + nope);	
} else {
  console.log("nama_kosong" + "\t" + nope);		
}
}