CoffeeScript Encapsulation and Variable Access

Question

Trying to understand how CoffeeScript instance and class variable works I came with this code (and the results are in the comments).

class A
  x: 1
  @y: 2

  constructor: (@z) -> 
    #console.log "const x", x #ReferenceError: x is not defined
    console.log "constructor y", @y #undefined
    console.log "constructor z", @z # = 3 for A and 6 for B

  get: () -> 
    #console.log "get x", x #ReferenceError: x is not defined
    console.log "get y", @y #undefined
    console.log "get z", @z # = 3 for A and 6 for B

  get2: () => 
    #console.log "get2 x", x #ReferenceError: x is not defined
    console.log "get2 y", @y #undefined
    console.log "get2 z", @z # = 3 for A and 6 for B

  @get3: () -> 
    #console.log "get3 x", x #ReferenceError: x is not defined
    console.log "get3 y", @y # = 2
    console.log "get3 z", @z #undefined

  @get4: () => 
    #console.log "get4 x", x #ReferenceError: x is not defined
    console.log "get4 y", @y # = 2
    console.log "get4 z", @z #undefined

class B extends A
  constructor: (@w) ->
    super(@w)

console.log '------A------'
i = new A 3
console.log "i.x", i.x # = 1
console.log "i.y", i.y #undefined
console.log "i.z", i.z # = 6
i.get()
i.get2()
A.get3()
A.get4()
console.log '------B------'
i = new B 6
console.log "i.x", i.x # = 1
console.log "i.y", i.y #undefined
console.log "i.z", i.z # = 6
console.log "i.w", i.w # = 6
i.get()
i.get2()
B.get3()
B.get4()
console.log '------------'

There are some strange things happening here:

x var I was expecting to access it from any method but x var can't be accessed from any method or constructor (ReferenceError). I'm only able to access it from a instance of A or B (i.x). Why is that?
@y var I was expecting to get @y var value from any method but it has no value in most of places (undefined value, not a ReferenceError exception). @y has value only on @get3 and @get4 (instance methods?). If it is defined, why I can't get its value?
@y and @z var Both @y and @z are instance variables, but because @z was initialized in the constructor, it has a differentiated behavior. @y is valid on @get3 and @get4 and @z is valid on get and get2. Again, what is happening here?

The thing is that I'm really confused by these behaviors. Is this code correct? So, should I learn more about JS generated by CS?

Tks

CoffeeScript Encapsulation and Variable Access

2 Answers