unobtrusive coffee script preloader

preloader.coffee

# by: _            _
#  __| |_ ___ _ __| |_  __ _ _ _    __ ___ _ __
# (_-<  _/ -_) '_ \ ' \/ _` | ' \ _/ _/ _ \ '  \
# /__/\__\___| .__/_||_\__,_|_||_(_)__\___/_|_|_|
#            |_|              stephan@stephan.com

# unobtrusive preloader

# applies to all elements with data-preload
# expects
# data-preload: array of image 
# data-order: loading order

$ ->
  # preload a series of images from filenames returning Image objects
  loadSeries = (filenames) ->
    _.map filenames, (filename) ->
      # console.log "load #{filename}"
      i = new Image()
      i.src = filename
      i

  # preload a series of images and attach them to a DOM element
  loadAndPrepend = (filenames, destination) ->
    _.each loadSeries(filenames), (image) ->
      $(destination).append(image)
      # $(image).hide()

  $('[data-preload]').hide()
    .sort (a, b) ->
      a.dataset.order > b.dataset.order
    .each (i, el) ->
      files = $(el).data('preload')

      # clear preload to make the DOM easier to read in the debugger
      # really not important, can be removed
      $(el).attr('data-preload', '[]') 

      loadAndPrepend(files, el)