A standalone copy of jQuery's extend(), in CoffeeScript

extend.coffee

# Adopted from: https://github.com/dansdom/extend
# Translated using js2coffee

extend = ->
  options = undefined
  name = undefined
  src = undefined
  copy = undefined
  copyIsArray = undefined
  clone = undefined
  target = arguments[0] or {}
  i = 1
  length = arguments.length
  deep = false
  objectHelper =
    
    # helper which replicates the jquery internal functions
    hasOwn: Object::hasOwnProperty
    class2type: {}
    type: (obj) ->
      (if not obj? then String(obj) else objectHelper.class2type[Object::toString.call(obj)] or "object")

    isPlainObject: (obj) ->
      return false  if not obj or objectHelper.type(obj) isnt "object" or obj.nodeType or objectHelper.isWindow(obj)
      try
        return false  if obj.constructor and not objectHelper.hasOwn.call(obj, "constructor") and not objectHelper.hasOwn.call(obj.constructor::, "isPrototypeOf")
      catch e
        return false
      key = undefined
      for key of obj
        {}
        
      key is `undefined` or objectHelper.hasOwn.call(obj, key)

    isArray: Array.isArray or (obj) ->
      objectHelper.type(obj) is "array"

    isFunction: (obj) ->
      objectHelper.type(obj) is "function"

    isWindow: (obj) ->
      obj? and obj is obj.window

  # end of objectHelper
  
  # Handle a deep copy situation
  if typeof target is "boolean"
    deep = target
    target = arguments[1] or {}
    
    # skip the boolean and the target
    i = 2
  
  # Handle case when target is a string or something (possible in deep copy)
  target = {}  if typeof target isnt "object" and not objectHelper.isFunction(target)
  
  # If no second argument is used then this can extend an object that is using this method
  if length is i
    target = this
    --i
  while i < length
    
    # Only deal with non-null/undefined values
    if (options = arguments[i])?
      
      # extend the base object
      for name of options
        src = target[name]
        copy = options[name]
        
        # Prevent never-ending loop
        continue  if target is copy
        
        # Recurse if we're merging plain objects or arrays
        if deep and copy and (objectHelper.isPlainObject(copy) or (copyIsArray = objectHelper.isArray(copy)))
          if copyIsArray
            copyIsArray = false
            clone = (if src and objectHelper.isArray(src) then src else [])
          else
            clone = (if src and objectHelper.isPlainObject(src) then src else {})
          
          # Never move original objects, clone them
          target[name] = extend(deep, clone, copy)
        
        # Don't bring in undefined values
        else target[name] = copy  if copy isnt `undefined`
    i++
  
  # Return the modified object
  target