changing props of reference type within function

reference_type_change_in_function.js

> const menu = {
... 'burger': 5.99,
... 'salad': 4.99,
... 'drink': 1.00
... }
undefined
> menu
{ burger: 5.99, salad: 4.99, drink: 1 }
> const addProperty = function addProperty(obj, prop, val) {
... obj[prop] = val
... console.log(`added ${prop} with val ${val} to the object`)
... }
undefined
> addProperty
[Function: addProperty]
> menu
{ burger: 5.99, salad: 4.99, drink: 1 }
> addProperty(menu, 'dessert of the day - cookie', '3.00')
added dessert of the day - cookie with val 3.00 to the object
undefined
> menu
{ burger: 5.99,
  salad: 4.99,
  drink: 1,
  'dessert of the day - cookie': '3.00' }
> addProperty(menu, entree, 15)
ReferenceError: entree is not defined
    at repl:1:19
    at realRunInThisContextScript (vm.js:22:35)
    at sigintHandlersWrap (vm.js:98:12)
    at ContextifyScript.Script.runInThisContext (vm.js:24:12)
    at REPLServer.defaultEval (repl.js:346:29)
    at bound (domain.js:280:14)
    at REPLServer.runBound [as eval] (domain.js:293:12)
    at REPLServer.onLine (repl.js:545:10)
    at emitOne (events.js:101:20)
    at REPLServer.emit (events.js:188:7)
> addProperty(menu, 'entree', 15)
added entree with val 15 to the object
undefined
> menu
{ burger: 5.99,
  salad: 4.99,
  drink: 1,
  'dessert of the day - cookie': '3.00',
  entree: 15 }
> addProperty(menu, 'entree number 2', 25)
added entree number 2 with val 25 to the object
undefined
> menu
{ burger: 5.99,
  salad: 4.99,
  drink: 1,
  'dessert of the day - cookie': '3.00',
  entree: 15,
  'entree number 2': 25 }
> menu.'dessert of the day' = 5
menu.'dessert of the day' = 5
     ^^^^^^^^^^^^^^^^^^^^
SyntaxError: Unexpected string

> menu['dessert of the day'] = 5
5
> menu
{ burger: 5.99,
  salad: 4.99,
  drink: 1,
  'dessert of the day - cookie': '3.00',
  entree: 15,
  'entree number 2': 25,
  'dessert of the day': 5 }