modal show not working after hide code example

Example 1: .show() and .hide not working for bootstrap modal

<button class="button primary" id="buy" style="text-decoration:none;" type="button">Review and confirm</button>

<div class="modal-bootstrap fade bs-example-modal-sm" id="myModal" tabindex="-1" role="dialog" aria-labelledby="smallModalLabel" aria-hidden="true">
    <!-- modal contents -->
</div>

<script type="text/javascript">
$("#buy").click(function () {
    var a = 4;
    if (a == 5) {
        alert("if");
        $('#myModal').modal('show');
    } else {
        alert("else");
        $('#myModal').modal('hide');
    }
});
</script>

Example 2: bs modal is working but not visible

<!-- Modal -->
<div id="myModal" class="modal fade" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
  <div class="modal-header">
    <button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button>
    <h3 id="myModalLabel">Modal header</h3>
  </div>
  <div class="modal-body">
    <p>One fine body…</p>
  </div>
  <div class="modal-footer">
    <button class="btn" data-dismiss="modal" aria-hidden="true">Close</button>
    <button class="btn btn-primary">Save changes</button>
  </div>
</div>

<a class="btn" data-target="#myModel" role="button" data-toggle="modal">Launch demo modal</a>

Example 3: modal.hide not working

function hideModal() {
  $("#myModal").removeClass("in");
  $(".modal-backdrop").remove();
  $('body').removeClass('modal-open');
  $('body').css('padding-right', '');
  $("#myModal").hide();
}