Using Task.jsm in SDK

task-in-sdk.js

const { Task } = Cu.import("resource://gre/modules/Task.jsm", {});
const { defer, all } = require("sdk/core/promise");
const { setTimeout } = require("sdk/timers");

Task.spawn(function *() {
  let item1 = yield getItem(1);
  let [item2, item3] = yield all([getItem(2), getItem(3)]);
  console.log(item1, item2, item3); // 1, 2, 3
}).then(function () {
  console.log('all items processed')
});

function getItem (val) {
  let { promise, resolve } = defer();
  setTimeout(() => resolve(val);
  return promise;
}