How to achive the logic below with the native JavaScript Promise implementation?

combine_requests.js

var requestPromise;
function getCurrentState() {
  // prevent sending multiple GET requests to /state.json. If one is pending, return its promise
  if (requestPromise.isPending()) return requestPromise;
  requestPromise = ajaxRequestReturningPromise('GET', '/state.json');
  return requestPromise;
}

promise1 = getCurrentState()
promise2 = getCurrentState()
// promise1 & promise2 send only one GET /state.json

function statusUpdater() {
    var pending = null;
    return function() {
        if (!pending) {
            pending = ajax("...");
            ajax.then(function() {
                pending = null;
            });
        }
        return pending;
    }
}

var getStatus = statusUpdater();

getStatus().then(...);
getStatus().then(...);

for reference, @jcoglan's fork https://gist.github.com/jcoglan/ff49998991022aad4e22