Javascript class attributes loaded async in constructor? - asynchronous

Question

I'm struggling with JavaScript async patterns to achieve this :
I have a class (I'm using CoffeeScript) with some attributes initialized in the constructor from some async calls. Then I have some methods that require these attributes to work. Here is a simplified example of what I'm trying to do :
# Class definition
class window.MyClass
constructor: ->
#attr = ... # loaded with an ajax call or whatever
myMethod: ->
console.log #attr
# User code
c = new MyClass()
c.myMethod() # should console.log the value loaded asynchronously
So the issue will be that when myMethod() is called, the async call hasn't finished yet.
I know a few solutions, however they imply moving the method call inside a callback (or a then function with promises). I want to avoid this to be able to call this method from click handlers or something else totally unrelated.
Also note that I can't move the async call inside my method since I will probably have several methods using the attribute, and I don't want to load the attr at each call, but only in the constructor.
Any idea ?

Answer 1

I finally found a way to do this. Not sure if it's very clean, but it works and fits my needs.
After loading asynchronously my attr value, I dispatch an event MyClassReady.
In my constructor, I've added a first listener to MyClassReady that sets an attribute ready to true.
Then, in myMethod, I wrapped my code in a function. Then I call this function if ready is true, otherwise I bind this function to the MyClassReady event.
The result looks like this :
# Class definition
class window.MyClass
constructor: ->
# Async load of `attr`
self = this
loadAttr (val) ->
self.attr = val
window.dispatchEvent new Event 'MyClassReady'
window.addEventListener 'MyClassReady', ->
self.ready = true
myMethod: ->
self = this
callback = ->
console.log self.attr
# If the attrs are already loaded
if #ready
callback()
else
window.addEventListener 'MyClassReady', ->
callback()
# User code
c = new MyClass()
c.myMethod() # this will wait until attr is loaded
I think it would be nice to move this code to a library, however with all the self = this stuff it seems complicated.
Edit: note that custom events aren't supported by IE...