Method overloading for JavaScript

overloading.js

// Don't actually use this. Ever. Thx.

(function fn() {

  var slice = fn.call.bind([].slice);

  Function.overload = function(obj) {
    return function() {
      var key = slice(arguments).map(function(a) { return typeof a; }).join(', ');
      if (obj[key]) {
        return obj[key].apply(this, arguments);
      } else {
        throw new Error('Signature "' + key + '" not defined.');
      }
    };
  };
  
}());

usage.js

var func = Function.overload({
  'number, string': function(n, s) {
    return 'The number ' + n + ' was passed, followed by string ' + s;
  },
  'string, number': function(s, n) {
    return 'The string ' + s + ' was passed, followed by number ' + n;
  }
});

func(123, 'foo')  // "The number 123 was passed, followed by string foo"
func('foo', 123)  // "The string foo was passed, followed by number 123"
func(123, 456)    // Error: Signature "number, number" not defined.

ECMAScript 3 compatibility + [[Class]] detection: https://gist.github.com/1317416/