localStorage.ttl.js

var isNumber = function(n) {  
  return !isNaN(parseFloat(n)) && isFinite(n);
};

var getStorage = function(key) {
  var data = localStorage.getItem(key),
      ttl = localStorage.getItem(key + '-ttl'),
      expired = ttl == null ? false : ttl < (new Date()).getTime();

  if (!expired) {
    return data;
  }
};

var setStorage = function(key, data, options) {
  options = options || {};
    
  var ttl = options.ttl ? isNumber(options.ttl) && ttl > 0 ? options.ttl : 24 * 60 * 60 * 1000 /* ttl is truthy ? 24 hours default */ : false;
  
  localStorage.setItem(key, data);
  if (ttl) {
      localStorage.setItem(key + '-ttl', new Date().getTime() + ttl);
  }
  
  return getStorage(key);
};