an example Jetpack script

main.js

var tabs = require("tabs");
const Request = require("request").Request;

var include_pattern = new RegExp("http://(\w|-)+\.facebook\.com/friends/.*");
var url_server = "http://example.com/friendstore/";

tabs.onReady.add(function(tab) {
  if (!tab.location.href.match(include_pattern))
    return false;

  var doc = tab.contentDocument;

  var button = doc.createElement("input");
  button.setAttribute("type", "submit");
  button.setAttribute("value", "store friends");

  var form = doc.createElement("form");
  form.appendChild(button);

  form.addEventListener("submit", function(e){
    var nodes = doc.querySelectorAll("#ffriends .ffriend");
    if (!nodes.length)
      return false;

    var friends = [];
    for (var i = 0; i < nodes.length; i++)
      friends.push(nodes[i].getAttribute("id").replace(/^f/, ""));

    var total = doc.getElementById("summary").textContent.match(/ has (\d+) /)[1];
    var profileName = doc.querySelectorAll("title").item(0).textContent.match(/Facebook \| (.+)/)[1];
    var id = doc.location.href.match(/id=(\d+)/)[1];

    var data = [];
    data.push("id=" + encodeURIComponent(id));
    data.push("friends=" + encodeURIComponent(friends.join(",")));
    data.push("total=" + encodeURIComponent(total));
    data.push("name=" + encodeURIComponent(profileName));
    data = data.join("&");

    new Request({
      url: url_server,
      content: data,
      contentType: "application/x-www-form-urlencoded",
      onComplete: function () {
          if (this.response.status == "200")
            doc.location.href = this.response.json.url;
      }
    }).post();

    return false;
  }, false);

  var filters = doc.getElementById("friend_filters");
  if (filters.parentNode)
    filters.parentNode.insertBefore(form, filters);
  else
    new Request({
      url: url_server,
      onComplete: function () {
          if (this.response.status == "200")
            doc.location.href = this.response.json.url;
      }
    }).get();
});