Accessing static properties in Coffeescript - coffeescript

Question

With the following code in mind
a.coffee
B = require './b'
C = require './c'
console.log B.someStaticVar
C.checkB()
b.coffee
C = require './c'
class B
#someStaticVar: 1
module.exports = B;
c.coffee
B = require './b'
class C
#checkB: ->
console.log B.someStaticVar
module.exports = C
I am trying to understand why the static property of b is undefined when accessed by c but returning 1 when accessed by a
Output:
$ coffee a.coffee
1
undefined

Answer 1

It looks like you have a circular reference.
A loads B
B loads C
C loads B
But B isn't done loading, so here it's an empty object
C finishes loading
B finishes loading
A loads C - it's already loaded so it just gets a reference.
A finishes loading, your console.log lines at the end of the file are executed.
Here is a version of your 3 modules that illustrates this better:
a.coffee
B = require './b'
C = require './c'
console.log B.someStaticVar
C.checkB()
b.coffee
C = require './c'
console.log 'in b.coffee, we have loaded C: ', C
class B
#someStaticVar: 1
module.exports = B;
c.coffee
B = require './b'
console.log 'in c.coffee, we have loaded B: ', B
class C
#checkB: ->
console.log B.someStaticVar
module.exports = C
You have two options for fixing this cyclic dependency in commonjs:
1. Lazy loading
Don't require ./b in c.coffee until you execute your function. By the time you call C.checkB inside a.coffee B will have been fully loaded and the correct class will be returned from the require call
class C
#checkB: ->
B = require './b'
console.log B.someStaticVar
module.exports = C
2. Refactoring
B and C are tightly coupled. Consider rewriting them to be contained within a single file. You could just remove the require './c' from b.coffee. Though I'm guessing it's in this example as your code is more complex and does have a need for it.
a.coffee
{ B, C } = require './b'
console.log B.someStaticVar
C.checkB()
b.coffee
class B
#someStaticVar: 1
class C
#checkB: ->
console.log B.someStaticVar
module.exports =
C: C
B: B