CoffeeScript: Method overloading

addMethod.coffee

# Via Jone Resig: http://ejohn.org/apps/learn/#90

addMethod (object, name, fn) ->
  # Save a reference to the old method 
  old = object[ name ]
 
  # Overwrite the method with our new one 
  object[ name ] = -> 
    # Check the number of incoming arguments, 
    # compared to our overloaded function 
    if fn.length is arguments.length
      # If there was a match, run the function 
      return fn.apply this, arguments
 
    # Otherwise, fallback to the old method 
    else if typeof old is "function"
      return old.apply this, arguments