sessionstorage ajax request using jquery

sessionstorage ajax request using jquery.js

var getCache = function(cacheKey, expireMinutes) {
  var value  = sessionStorage.getItem(cacheKey);
  var timestamp = Math.floor(Date.now() / 1000);
  var expireTime = timestamp - (expireMinutes * 60);
  var data = null;
  if (value === null) {
      return null;
  }
  data = JSON.parse(value);
  if (typeof data !== 'object') {
      return null;
  }
  if (data.created < expireTime) {
      sessionStorage.removeItem(cacheKey);
      return null;
  }
  return data;
};
var setCache = function(cacheKey, value) {
  var timestamp = Math.floor(Date.now() / 1000);
  var data  = {
      value: value,
      created: timestamp
  };
  sessionStorage.setItem(cacheKey, JSON.stringify(data));
}
var getData = function(url, cache) {
  var cacheKey = 'cache_' + url;
  var data = getCache(cacheKey, 15);
  if (cache && data !== null) {
      var d = $.Deferred();
      d.resolve(data.value);
      return d.promise();
  }
  return $.get(url).done(function(response) {
      if (cache) {
          setCache(cacheKey, response)
      }
  });
};