CoffeeScript class results in empty object

Question

I have a file 'a.coffee', with the following code:

class Options
  options:
    # ...

  setOption: (name, value) ->
    # ...

  getOption: (name) ->
    # ...

# Export the Options class.
module.exports = Options

And file 'b.coffee':

Options = require './a'
console.log new Options()

Of course, it is expected that when I run b.coffee, I will see this output:

{
  options: ...,
  setOption: function (name, value),
  getOption: function (name)
}

But instead, I get {}.

How can I fix this?

mu is too short · Accepted Answer · 2015-08-10 17:54:26Z

3

Your expectations are wrong. Everything at the class level goes in the object's prototype so given this:

class C
  p: 6
  m: ->
o = new C

the object o will be empty because there are no instance variables but if you look at the "class" (via Object.prototype.constructor to get the "class" and :: to get the prototype):

o.constructor::p

you'll see things.

If you add some instance variables (i.e. something that really is part of your object):

class C
  constructor: -> @p = 6

then you'll see them in the object:

c = new C
console.log c
# { p: 6 } will appear in the console

answered Aug 10, 2015 at 17:54

mu is too short

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5 Comments

Ethan McTague Over a year ago

But this seems to go against what is demonstrated at coffeescript.org/#classes

mu is too short Over a year ago

How so? I don't see any discrepancies. You can o = new Options; o.getOption('x') just fine due to prototypical inheritance.

Ethan McTague Over a year ago

Then it seems the problem I am having is different from what I thought - I had a more detailed class here: raw.githubusercontent.com/htmlguy/elapse/master/src/… and nodejs was reporting an error when the getOption function is called. I suppose I'll have to make a new question for my real problem.

mu is too short Over a year ago

I don't see anything obviously wrong with your getOption. BTW, "wether" is a ram or goat with a certain anatomical modification, the word you're looking for is "whether".

Ethan McTague Over a year ago

Thank you. I fixed the actual problem on my own, still not sure exactly what it was.

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