Formal – Interruption free communication(formalapp.com)

  // For a given domain, localStorage uses the same permissions as cookies.  When
  // cookies are blocked, attempts to access localStorage will throw a Security
  // exception.  We do that test once here so that we can safely test for this
  // object everywhere else.
  define(function() {
  	try {
  		var K = '__test', V = 1, s = window.localStorage;
  		if (s) {
  			s.setItem(K, V);
  			if (V == s.getItem(K)) {
  				s.removeItem(K);
  				return s;
  			}
  		}
  	} catch(e) {}
  	
  	return null;
  });