Question

class Example
  constructor: ->
    $.each [1, 2, 3], (key, value) ->
      @test = value
    return @test
  render: ->
    alert @test

example = new Example()
example.render()​​​​​​​​​​​​​​​​​​​​​​

I’m using CoffeeScript (+ jQuery) and this is an class example where I would get the value 3 in @test variable. But this does not happen, can you help me?

Answer 1

This is a scoping problem:
$.each accepts a function, which has it’s on scope, thus, your this variable is not the one you expected.

The working code:

class Example
  constructor: ->
    $.each [1, 2, 3], (key, value) =>
      @test = value
    return @test
  render: ->
    alert @test

example = new Example()
example.render()​​​​​​​​​​​​​​​​​​​​​​

What changed? Check the arrow on the $.each call, it’s now a fat arrow. Fat arrows does the trick of setting a _this variable and using it when you use @... making your scope the one you expected to be.

Check http://coffeescript.org on the section “Function Binding” for more details!