coffee scrip - relative and fixed positioning dependant on if div is viewable on screen

coffee script - relativefixed positioning

# code for the advert preview and the "why go premium list" on the create new ad form so that it only adopts fixed positioning when all of it is in view.

$ ->
  e = $("div#advert_preview")
  jWindow = $(window)
  offsetTop = e.offset().top
  positionTop = e.position().top
  jWindow.scroll ->
    if jWindow.scrollTop() > offsetTop
      e.css
        position: "fixed"
        top: 0
    else
      e.css
        position: "relative"
        top: positionTop

gistfile1.txt

# code for the advert preview and the "why go premium list" on the create new ad form so that it only adopts fixed positioning when all of it is in view.

$ ->
  e = $("div#advert_preview")
  jWindow = $(window)
  offsetTop = e.offset().top
  positionTop = e.position().top
  jWindow.scroll ->
    if jWindow.scrollTop() > offsetTop
      e.css
        position: "fixed"
        top: 0
    else
      e.css
        position: "relative"
        top: positionTop