Class Method that Constructs a New Instance

Question

I'd like to emulate ActiveRecord scopes on a CoffeeScript class.

What's tripping me up is the context when defining the @scope function. The @scope function itself should execute in the context of the underlying class, but the function it is passed should operate in the context of that instance.

Here is what I have, but the popped function ends up running in the context of Window instead of the instance that called it.

class Collection
  models: []

  @scope: (name, funct) ->
    @.prototype[name] = ->
      new @constructor(funct())

  constructor: (models) ->
    @models = models

class Bubbles extends Collection
  @scope 'popped', ->
    @models.slice(1, @models.length)

  first: ->
    @models[0]


console.log(new Bubbles([1,2,3,4]).popped()) # should return an instance of Bubbles with models == [2,3,4]

mu is too short · Accepted Answer · 2013-11-22 01:51:19Z

2

The problem is that you're calling funct as a simple function:

new @constructor(funct())

so @ inside funct is going to be window. You can use apply or call to specify what @ should be (i.e. to call the function as a method):

@scope: (name, funct) ->
  @::[name] = ->
    new @constructor(funct.apply(@))

Note that I've also switched to :: as that's more idiomatic CoffeeScript that prototype.

Demo: http://jsfiddle.net/ambiguous/9Pmcr/

answered Nov 22, 2013 at 1:51

mu is too short

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