cocoon_limit.coffee

class CocoonLimit
  constructor: (@$cocoon) ->
    @limit = parseInt(@$cocoon.data("cocoon-limit"))
    @$cocoon.on "cocoon:after-insert", @toggleAddButton
    @$cocoon.on "cocoon:after-remove", @toggleAddButton
    @toggleAddButton()

  toggleAddButton: =>
    hide = @$cocoon.find(".nested-fields:visible").length >= @limit
    @$cocoon.find(".add_fields").toggleClass("hidden", hide)

  @init: ->
    $("[data-cocoon-limit]").each ->
      new CocoonLimit($(this))

$ ->
  CocoonLimit.init()

form.html.haml

%h3
  Images
  %small (max 4)
#images{ "data-cocoon-limit" => 4 }
  = f.simple_fields_for :images do |image|
    = render 'image_fields', f: image
  .links
    = link_to_add_association 'Add Image', f, :images, class: 'btn btn-default btn-sm'