Wrapper to add optional TTL for localStorage.

LocalStore.js

// polyfill for localstorage into stale storage so this data store doesnt ever fail
if (!('localStorage' in window)) {
//if (!Modernizr.localstorage) {
  window.localStorage = {
    _data       : {},
    setItem     : function(id, val) { return this._data[id] = String(val); },
    getItem     : function(id) { return this._data.hasOwnProperty(id) ? this._data[id] : undefined; },
    removeItem  : function(id) { return delete this._data[id]; },
    clear       : function() { return this._data = {}; }
  };
}


// localstorage interface
// handles parsing JSON strings, etc
var DataStore = (function() {

  // returns the value associated with the given key, if it exists
  // returns null if the key doesn't exist
  function getItem(name) {
    var item = localStorage.getItem(name);

    if (item) {
      try {
        item = JSON.parse(item);
      } catch (err) {
        console.warn(err);
      }
    }

    return item;
  }

  // saves a new name/value pair if the key doesn't exist, otherwise
  // updates the value
  function setItem(name, value) {
    try {
      value = JSON.stringify(value);
    } catch (err) {
      console.warn(err);
    }
    
    return localStorage.setItem(name, value);
  }

  function set(name, value, ttl) {
    if (ttl != null) ttl = +new Date() + ttl;

    var item = {
      value: value,
      ttl: ttl
    };

    return setItem(name, item);
  }

  function get(name) {
    var item = getItem(name);

    // if there's a expired ttl, remove the item
    if (item && item.ttl && item.ttl < +new Date()) {
      return removeItem(name);
    }

    return item && item.value;
  }

  // remove an item from local storage
  function removeItem(name) {
    return localStorage.removeItem(name);
  }

  // delete all name/value pairs currently stored
  function clear() {
    return localStorage.clear();
  }

  return {
    get: get,
    set: set,
    remove: removeItem,
    clear: clear
  };

})();