storage.js

function storageGet() {
  var res;
  chrome.storage.local.get(res = callbackFunc(items));
  console.log(res);
  return res;
}

function callbackFunc(items) {
  console.log(items);
  callback(items);
}

const items = storageGet();

普通に

function postPlayLists() {
  const playlists = storageGet(() => { /* なんかする */});
}

やで