bootstrap modal safeshow

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/2.3.2/css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/2.3.2/js/bootstrap.min.js"></script>
        <button id="b2">open</button>

<div id="modal1" class="modal">
    <div>
        hello world
        <button id="b1">reopen</button>
        <button id="close">close</button>
    </div>
</div>

JavaScript

$.fn.modal.Constructor.prototype.safeShow = function() {
    var that = this;
    if (this.$backdrop) {
      this.$element.one('hidden', 
        function(){that.show()});
    } else {
      this.show();
    }
}
$("#modal1").modal('safeShow');