overloading functions in javascript (from DailyJS)

overload.js

var __slice = [].slice
var __toString = {}.toString
var __noop = function (){}

function typeOf(x) {
  return __toString.call(x).slice(8,-1)
}

function overload(fs) {
  return function () {
    var type = __slice.call(arguments).map(typeOf).join('_')
    var f = fs[type] || __noop
    return f.apply(this, arguments)
  }
}

var fn = overload({
      String: function (s) {
        return 'Hello '+ s
      },
      Number: function (x) {
        return x * x
      },
      Array_Function: function (xs, f) {
        return xs.map(f)
      },
      RegExp_String_Number: function (re, s, x) {
        return s.replace(re, x)
      }
    })

console.log(fn('Joe'))
//=> "Hello Joe"
console.log(fn(3))
//=> 9
console.log(fn([1,2,3], function(x){ return x+1 }))
//=> [2,3,4]
console.log(fn(/a/g, 'wawa', 2))
//=> "w2w2"