a jquery plugin to pin an element on any element u want

pin.coffee

do ($=jQuery) ->
  $.fn.pin = (target) ->
    $target = if target
      if typeof target == "function"
        target.apply @
      else
        $(target)
    else
      $(@).parent()

    originTop = $(@).offset().top
    targetBottom = $target.offset().top + $target.height()
    $(window).scroll =>
      if ($(@).offset().top + $(@).height()) > targetBottom
        $(@).css
          position: "absolute"
          top: targetBottom - $(@).height()
        return
      if $(@).offset().top < originTop
        $(@).css
          position: "static"
        return
      if $(@).offset().top < $(window).scrollTop() and ($(@).offset().top + $(@).height()) < targetBottom
        $(@).css
          position: "fixed"
          top: 0
        return
      if $(@).offset().top > $(window).scrollTop() and $(@).offset().top > originTop
        $(@).css
          position: "fixed"
          top: 0
        return