Check if element is visible in viewport and scroll if necessary

gistfile1.coffee

$.extend $.expr[":"],
  inView: (a) ->
    # cf. http://remysharp.com/2009/01/26/element-in-view-event-plugin/#comment-127058
    st = (document.documentElement.scrollTop or document.body.scrollTop)
    ot = $(a).offset().top
    wh = (if (window.innerHeight and window.innerHeight < $(window).height()) then window.innerHeight else $(window).height())
    ot > st and ($(a).height() + ot) < (st + wh)

$.fn.scroll_if_necessary = ->
  if this.length && not @is(":inView")
    $("body").animate({scrollTop: $(this).offset().top}, 200)