When using this .js 2 times on a single page it only works in the one instance
<p>This script creates menu tabs above a text area. The script works if use only once on a page, I however need to use it twice on a single page, to create 2 text areas, each with a menu above them. As soon as I use it twice only one instance works. Any suggestions. </p>

<pre><code>window.onload=function() {

  // get tab container
  var container = document.getElementById("tabContainer");
    // set current tab
    var navitem = container.querySelector(".tabs ul li");
    //store which tab we are on
    var ident = navitem.id.split("_")[1];
    navitem.parentNode.setAttribute("data-current",ident);
    //set current tab with class of activetabheader
    navitem.setAttribute("class","tabActiveHeader");

    //hide two tab contents we don't need
    var pages = container.querySelectorAll(".tabpage");
    for (var i = 1; i &lt; pages.length; i++) {
      pages[i].style.display="none";
    }

    //this adds click event to tabs
    var tabs = container.querySelectorAll(".tabs ul li");
    for (var i = 0; i &lt; tabs.length; i++) {
      tabs[i].onclick=displayPage;
    }
}

// on click of one of tabs
function displayPage() {
  var current = this.parentNode.getAttribute("data-current");
  //remove class of activetabheader and hide old contents
  document.getElementById("tabHeader_" + current).removeAttribute("class");
  document.getElementById("tabpage_" + current).style.display="none";

  var ident = this.id.split("_")[1];
  //add class of activetabheader to new active tab and show contents
  this.setAttribute("class","tabActiveHeader");
  document.getElementById("tabpage_" + ident).style.display="block";
  this.parentNode.setAttribute("data-current",ident);
}
</code></pre>
