Detect availability of Web Storage

storage-available.js

/**
 * Checks whether a storage mechanism is available.
 * @param {String} storageType: it can be "localStorage", "sessionStorage" or any global object that implements Web Storage interface.
 * @return {Boolean}
 */
function storageAvailable(storageType) {
  var storage = window[storageType];
  var data = '__proxy-storage__';
  try {
    storage.setItem(data, data);
    storage.removeItem(data);
    return true;
  }
  catch(e) {
    return false;
  }
}

usage.js

// tests availability of global objects
// that implement Web Storage interface
if (storageAvailable('localStorage')) {
  // you can use Web Storage
}
else {
  // private mode or unavailable
}

If you want to be able to treat all cases the same, whether storage is actually available or not, you can shim the local storage API by using a polyfill. I can recommend memorystorage as it's written by a very friendly author ;)

For example:

//Web Storage aliases
var _localStorage = storageAvailable('localStorage') ? window.localStorage : new MemoryStorage('local');
// from here on, _localStorage will just work, whether it's actually available or not. 
// However data will be gone as soon as the page is refreshed.

@Download Thank you for your feed back!