getCache.js

var getCache = (function() {
  var supportsLocalStorage = 'localStorage' in window,
      cache = {};

  function getJSON(key) {
    return jQuery.getJSON(key).then(function(data) {
      cache[key] = data;
      localStorage.setItem(key, JSON.stringify(data));
    }).promise();
  }

  function getStorage(key) {
    var storedData = localStorage.getItem(key);
    return storedData ? finish(JSON.parse(storedData)) : getJSON(key);
  }

  function finish(data) {
    var dfd = new jQuery.Deferred();
    setTimeout(function() {
      dfd.resolveWith(null, [data]);
    });
    return dfd.promise();
  }

  return function(key) {
    if (cache[key]) finish(key);
    return supportsLocalStorage ? getStorage(key) : getJSON(key);
  };

}());