JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://raw.github.com/dperini/ContentLoaded/master/src/contentloaded.js"></script>
<header class="container">
  <a href="index" class="brand"><div class="logo"></div></a>
  <nav>
    <a href="index" class="active">Home</a> |
    <a href="about-us" class="active">About Us</a> |
    <a href="contact-us" class="active">Contact Us</a>
  </nav>
</header>

CSS

.active { color: aqua }

JavaScript

(function(window, document, undefined) { contentLoaded(window, function() {

  //var page = document.location.pathname.match(/[A-z]+$/)[0],
    var page = 'http://example.com/index',
      nav_anchors = document.getElementsByTagName('header')[0]
                            .getElementsByTagName('nav')[0]
                            .getElementsByTagName('a');
  
  for(i in nav_anchors)
    if(nav_anchors[i].href.match(/[A-z]+$/)[0] = page)
      nav_anchors[i].classList.add('active');

})
})(this, this.document)