SO http://is.gd/JvjIp6

by ecupaio

HTML

<link rel="stylesheet" href="//netdna.bootstrapcdn.com/bootstrap/3.1.1/css/bootstrap.min.css">
<script src="//netdna.bootstrapcdn.com/bootstrap/3.1.1/js/bootstrap.min.js"></script>
<nav class="navbar navbar-default navbar-fixed-top " role="navigation">
    <div class="container-fluid">
        <!-- Brand and toggle get grouped for better mobile display -->
        <div class="navbar-header">
            <button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1"> <span class="sr-only">Toggle navigation</span>
 <span class="icon-bar"></span>
 <span class="icon-bar"></span>
 <span class="icon-bar"></span>

            </button> <a class="navbar-brand" href="#">Brand</a>

        </div>
        <!-- Collect the nav links, forms, and other content for toggling -->
        <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
            <ul class="nav navbar-nav">
                <li class="active"><a href="#">Link</a>
                </li>
                <li><a href="#">Link</a>
                </li>
                <li class="dropdown"> <a href="#" class="dropdown-toggle" data-toggle="dropdown">Dropdown <b class="caret"></b></a>

                    <ul class="dropdown-menu">
                        <li><a href="#">Action</a>
                        </li>
                        <li><a href="#">Another action</a>
                        </li>
                        <li><a href="#">Something else here</a>
                        </li>
                        <li class="divider"></li>
                        <li><a href="#">Separated link</a>
                        </li>
                        <li class="divider"></li>
                        <li><a href="#">One more separated link</a>
                        </li>
                    </ul>
                </li>
            </ul>
            <form class="navbar-form navbar-left" role="search">
                <div class="form-group">
          ...

CSS

body {
    /* for demo purpose only */
    height:2000px;
    padding-top:100px;
}

JavaScript

(function ($) {
  $(document).ready(function(){
	$(function () {
		$(window).scroll(function () {
			if ($(this).scrollTop() > 100) {
				$('.navbar').fadeOut();
			} else {
				$('.navbar').fadeIn();
			}
		});
	});
});
  }(jQuery))