Position div depending on distance browser edge (javascript)

var $doc = $(document),
    $win = $(window),
    $this = $('#mydiv'),
    offset = $this.offset(),
    dTop = offset.top - $doc.scrollTop(),
    dBottom = $win.height() - dTop - $this.height(),
    dLeft = offset.left - $doc.scrollLeft(),
    dRight = $win.width() - dLeft - $this.width();