Question

I want to improve a small framework, and therefore I want to get rid of two calls to eval.

Let the code speak:

# irf.coffee (The Framework)
# Classes which are appended to the namespace 'IRF'
classes = [
  "Background"
  "BoundingBox"
  # ...
]

# Namespace where to attach classes
@IRF = {}

# TODO: Get rid of eval(c)
for c in classes
  @IRF[c] = eval(c)

I only want the IRF to ‘pollute’ the global namespace so I could access classes/objects like new IRF.Background().

The goal of this framework is to be used by other projects including this framework.
So I might have a project like this:

class TowerMap extends IRF.Game
  constructor: (width, height) ->
    @background = new IRF.Background(width, height)

As you see, I have to use the IRF namespace here, but within this particular project I’d like to use it without the namespace, as I did this:

# Require all Class of IRF, so we won't need namespace here
# TODO: get rid of eval
eval("var #{k} = v") for k,v of IRF

class TowerMap extends Game
  constructor: (width, height) ->
    @background = new Background(width, height)

Everything works as expected, but somehow those two evals disturb me.
Might there be another solution?

Answer 1

Why not just import the bits you need?

Background = IRF.Background

class TowerMap extends Game
  constructor: (width, height) ->
    @background = new Background(width, height)

You should be aware that eval in EcmaScript 5 strict mode can’t introduce new variable declarations so eval('var x = ...') in strict mode will not make a variable that is visible to surrounding non-eval code.

EcmaScript 5 Appendix C says

Strict mode eval code cannot instantiate variables or functions in the variable environment of the caller to eval. Instead, a new variable environment is created and that environment is used for declaration binding instantiation for the eval code (10.4.2).