Subscribe to Online / Offline Changes

subscribe-online.js

// subscribe to online / offline events
// (bool -> undefined) -> () -> undefined
const subscribeOnline = (cb) => {
  const online = () => cb(true);
  const offline = () => cb(false);
  window.addEventListener('online', online, false);
  window.addEventListener('offline', offline, false);
  
  return function unsubscribe() {
    window.removeEventListener('online', online);
    window.removeEventListener('offline', offline);
  };
};


/* usage */

// subscribe
const unsub = subscribeOnline((online) => {
  console.log(`Online? ${ online }`);
});

// unsubscribe
unsub();