Hello i need help with javascript on how to show and hide ads as i ont know much about javascript

<h2>Hide Div in JavaScript</h2>
<script language=javascript type='text/javascript'> 
function hideDiv() { 
if (document.getElementById) { 
document.getElementById('div').style.visibility = 'hidden'; 
function showDiv() { 
if (document.getElementById) { 
document.getElementById('div').style.visibility = 'visible'; 
<body onload="javascript:showDiv()">
<button onclick="javascript:hideDiv()">Hide</button> 
<button onclick="javascript:showDiv()">Show</button>

<div id="div">

<script type="text/javascript"><!--
google_ad_client = "ca-pub-xxxxxxxx";
google_ad_slot = "xxxxxxx";
google_ad_width = 300;
google_ad_height = 250;
<script type="text/javascript"


Above code works if i put hellow world between div but it doeesnt if i put ad code. ads never get hide

ads never get hide

Probably in the Google script. I don't think hiding ads is allowed by the ToS.