simple, but production ready implementation of memoisation in js

memo.coffee

do () ->
  getStorage = () ->
    storage =
      values: {}
      isStored: (key) ->
        key of @values
      getValue: (key) ->
        @values[key]
      store: (key, value) ->
        @values[key] = value
    storage
  memo = (origFn) ->
    storage = getStorage()
    wrappedFn = (key) ->
      if storage.isStored key
        return storage.getValue key
      value = origFn.apply this, arguments
      storage.store key, value
      value
  @memo = memo

memo.js

(function() {
    function getStorage() {
        var storage = {
            values: {},
            isStored: function(key) {return key in storage.values},
            getValue: function(key) {return storage.values[key]},
            store: function(key, value) {storage.values[key] = value}
        }
        return storage
    }
    function memo(origFn) {
        var storage = getStorage()
        var wrappedFn = function(key) {
            if (storage.isStored(key)) {
                return storage.getValue(key)
            }
            var value = origFn.apply(this, arguments)
            storage.store(key, value)
            return value
        }
        return wrappedFn
    }
    this.memo = memo
})(this)