Edit in JSFiddle

window.addEventListener("load", function() {
			makeTabs(".tabs")
});

function makeTabs(selector) {

    tab_lists_anchors = document.querySelectorAll(selector + " li a");
    divs = document.querySelector(selector).getElementsByTagName("div");
    for (var i = 0; i < tab_lists_anchors.length; i++) {
        if (tab_lists_anchors[i].classList.contains('active')) {
            divs[i].style.display = "block";
        }

    }

    for (i = 0; i < tab_lists_anchors.length; i++) {

        document.querySelectorAll(".tabs li a")[i].addEventListener('click', function(e) {

            for (i = 0; i < divs.length; i++) {
                divs[i].style.display = "none";
            }

            for (i = 0; i < tab_lists_anchors.length; i++) {
                tab_lists_anchors[i].classList.remove("active");
            }

            clicked_tab = e.target || e.srcElement;

            clicked_tab.classList.add('active');
            div_to_show = clicked_tab.getAttribute('href');

            document.querySelector(div_to_show).style.display = "block";

        });
    }

}

<div class="tabs">
				<ul>
				<li><a href="#tab1" class="active">Tab 1</a></li>
				<li><a href="#tab2">Tab 2</a></li>
				<li><a href="#tab3">Tab 3</a></li>
			</ul>
			<div id="tab1">
				<h1>Tab 1</h1>
				<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Accusamus nihil illo nobis sunt dolor iure nulla perferendis reprehenderit mollitia inventore laudantium cum deserunt quisquam esse excepturi aliquam eius cumque numquam.</p>
			</div>
			
			<div id="tab2">
				<h1>Tab 2</h1>
				<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Cumque id iste quo quisquam hic dicta natus porro voluptatum illo in doloribus eligendi itaque vitae reprehenderit fugiat enim vero a sunt.</p>
			</div>
			
			<div id="tab3">
				<h1>Tab 3</h1>
				<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Fuga porro amet voluptates dolorem hic minima officiis sed quae esse laborum eveniet maiores voluptatem architecto aspernatur aliquid nihil repellendus atque praesentium.</p>
			</div>
		</div>
		

.tabs{
  overflow:hidden;
  clear:both;

}
.tabs ul{
  list-style-type:none;
  bottom: -1px;
  position:relative;
}
.tabs li{
  float:left;
}

.tabs a{
  display:block;
  padding:5px 10px;
  background-color: #EEE;
  color: #000;
  text-decoration: none;
  margin: 0 4px;
  border-top:1px solid #CCC;
  border-left:1px solid #DDD;
  border-right:1px solid #DDD;
  font:13px/18px verdana,arial,sans-serif;
  border-bottom:1px solid #CCC;
}
.tabs a.active{
  background-color: #fff;
  border-bottom:1px solid #fff;
}
.tabs div{
  clear: both;
  border:1px solid #CCC;
  padding:5px;
  font-family:verdana;
  font-size:13px;
  background-color: #fff;
  display:none;
}