Highlight current page on navbar

nav.php

@@ -5,10 +5,21 @@
         </div>
         <div id="navbar" >
             <ul class="nav navbar-nav">
-                <li><a href="Routes.php">Routes</a></li>
+                <li class="<?php echo isActive("/Routes.php");?>" ><a href="/Routes.php">Routes</a></li>
-                <li><a href="Stops.php">Stops</a></li>
+                <li class="<?php echo isActive("/Stops.php");?>"><a href="/Stops.php">Stops</a></li>
             </ul>
         </div>
     </div>
 </nav>
 <div class="container">
+
+<?php
+
+function isActive($url){
+    if ($_SERVER['PHP_SELF'] == $url){
+        return ' active ';
+    }
+    return;
+}
+
+?>