Object.toType

ba-objecttotype.js

// See http://javascriptweblog.wordpress.com/2011/08/08/fixing-the-javascript-typeof-operator/

(function(global) {
  // Maintain a map of already-encountered types for super-fast lookups. This
  // serves the dual purpose of being an object from which to use the function
  // Object.prototype.toString for retrieving an object's [[Class]].
  var types = {};

  // Return a useful value based on a passed object's [[Class]] (when possible).
  Object.toType = function(obj) {
    var key;
    // If the object is null, return "Null" (IE <= 8)
    return obj === null ? "Null"
      // If the object is undefined, return "Undefined" (IE <= 8)
      : obj == null ? "Undefined"
      // If the object is the global object, return "Global"
      : obj === global ? "Global"
      // Otherwise return the XXXXX part of the full [object XXXXX] value, from
      // cache if possible.
      : types[key = types.toString.call(obj)] || (types[key] = key.slice(8, -1));
  };
}(this));

I know this is ancient code, but for anyone stumbling on this today (mid 2014), note that PhantomJS currently returns "DomWindow" for both undefined and null (it's a known bug, but still)