Add the script tag in index.html (or other page you want to use it) like this:
<script style="text/javascript" src="navLoader.js"></script>
Delete all the navbar code from index.html (or other pages that will use the navbar) and replaced with:
<div class="navbar-frame"></div>
Create a navbar.html file with all the navbar code:
<!--Header bar!-->
<nav class="navbar navbar-default navbar-fixed-top">
<div class="container">
<div class="navbar-header">
<button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navbar" aria-expanded="false" aria-controls="navbar">
<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="/index.html">Your Stuff</a>
</div>
<div id="navbar" class="navbar-collapse collapse">
<ul class="nav navbar-nav">
<li class="background-header"><a href="#">Test 1</a></li>
<li class="background-header"><a href="#">Test 2</a></li>
<li class="dropdown">
<a href="#" class="dropdown-toggle background-header" data-toggle="dropdown" role="button" aria-expanded="false">Projects <span class="caret"></span></a>
<ul class="dropdown-menu" role="menu">
<li class="dropdown-header dropdown-divisor">Java</li>
<li class="background-header"><a href="/TEXTLAND/Textlandrpg.html">TEXTLAND textual RPG</a></li>
<li class="divider"></li>
<li class="dropdown-header dropdown-divisor">HTML5 & Javascript</li>
<li class="background-header"><a href="#">Another test</a></li>
<li class="divider"></li>
<li class="dropdown-header dropdown-divisor">HTML/CSS</li>
<li class="background-header"><a href="/CSSolarSystem/SolarSystemHTMLCSS.html">CSSolar System</a></li>
</ul>
</li>
</ul>
<ul class="nav navbar-nav navbar-right">
<li class="background-header">
<a href="#">Contact
<span class="sr-only">(current)</span>
</a>
</li>
<li class="background-header"><a href="#">Leave a comment</a></li>
</ul>
</div><!--/.nav-collapse -->
</div>
</nav>
and then create a navLoader.js file with this .load method:
$(document).ready(function(){
$("#navbar-frame").load("navbar.html");
});
Every time the page is fully loaded, it will go to navLoader.js get the navbar.html and load it inside the .navbar-frame div. Now, if you need to change something in the navbar, just change the navbar.html file.
And of course, change the li tags as you need, this is just an example.
(using jQuery)