Proximity loading for images/social scripts

proximity_loader.coffee

# Really this is just a proximity_sensor, it will fire whatever event you pass as an arg
# It has nothing to do with loading, that's just how we've used it so far

required = if window.lp.isMobile then 'jsmin' else 'jquery'

define [required, 'lib/extends/events'], ($, EventEmitter) ->

  class ProximityLoader

    for key, value of EventEmitter
      @prototype[key] = value

    LISTENER = '#js-row--content'

    # params
    # el: The listening element
    # list: comma delimited list of elements to watch
    # success: event to fire when the criteria is matched
    # klass: Custom parameters to pass through with the success event
    constructor: (args) ->
      @success = args.success || ':asset/uncomment'
      @klass = args.klass
      @$el = $(args.el || LISTENER)
      return false if @$el.length is 0

      @elems = @_setUpElems(args)
      @_check() # Check on load in case the user refreshes midway down the page
      @_watch()


    # Private

    _getViewportEdge: ->
      scrolled =  if window.pageYOffset then window.pageYOffset else document.documentElement.scrollTop
      scrolled + document.documentElement.clientHeight

    _setUpElems: (args) ->
      elems = []
      for el in args.list.split(',')
        $elems = @$el.find(el)
        for $el in $elems
          $el = if $.fn then $($el) else $el
          elems.push({
            $el: $el
            top: parseInt($el.offset().top, 10)
            threshold: parseInt($el.data('threshold') || 500, 10)
          })
      elems

    _watch: ->
      enableTimer = false
      # Only create jquery object if necessary, otherwise we already have the node
      win = if $.fn then $(window) else window
      win.on 'scroll', =>
        clearTimeout(enableTimer) if enableTimer
        enableTimer = setTimeout =>
          @_check()
        , 200

    _check: () ->
      if @elems.length > 0
        newElems = []
        fold = @_getViewportEdge()
        for el in @elems
          if (el.top - el.threshold) <= fold
            @trigger(@success, [el.$el, @klass])
          else
            newElems.push(el)
        # Create a new array of elements that have not yet matched
        @elems = newElems