toType() by Angus Croll

to-type.js

var toType = function(obj) {
  return ({}).toString.call(obj).match(/\s([a-zA-Z]+)/)[1].toLowerCase()
}

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"

/***
We could get a little cleverer (inspired by Chrome’s use 
of “global” for window.[[Class]]). By wrapping the 
function in a global module we can identify the 
global object too:
***/

Object.toType = (function toType(global) {
  return function(obj) {
    if (obj === global) {
      return "global";
    }
    return ({}).toString.call(obj).match(/\s([a-z|A-Z]+)/)[1].toLowerCase();
  }
})(this)