If you know Javascript, then this isn’t a suprise:

typeof {a: 4}; //"object"
typeof [1, 2, 3]; //"object"
(function() {console.log(typeof arguments)})(); //object
typeof new ReferenceError; //"object"
typeof new Date; //"object"
typeof /a-z/; //"object"
typeof Math; //"object"
typeof JSON; //"object"
typeof new Number(4); //"object"
typeof new String("abc"); //"object"
typeof new Boolean(true); //"object"

But thanks to some dilligent work by one Angus Croll, you can do something like:

toType({a: 4}); //"object"
toType([1, 2, 3]); //"array"
(function() {console.log(toType(arguments))})(); //arguments
toType(new ReferenceError); //"error"
toType(new Date); //"date"
toType(/a-z/); //"regexp"
toType(Math); //"math"
toType(JSON); //"json"
toType(new Number(4)); //"number"
toType(new String("abc")); //"string"
toType(new Boolean(true)); //"boolean"

Check out the full explanation @
http://javascriptweblog.wordpress.com/2011/08/08/fixing-the-javascript-typeof-operator/