var tabs = ["tab1","tab2"];

  function showTab( tab ){

    // first make sure all the tabs are hidden
    for(i=0; i < tabs.length; i++){
      var obj = document.getElementById(tabs[i]);
      obj.style.display = "none";
    }
      
    // show the tab we're interested in
    var obj = document.getElementById(tab);
    obj.style.display = "block";

  
  }