hi i have a css style button with following code,

but my cms seems to be stripping the javascript , is there some alternative to link the button?

Code:
<h2 class="black-first-title"><button class="button yellow" onclick="javascript:document.location='/joomla/index.php/webshop/cart/add?quantity[0]=1&amp;virtuemart_product_id[0]=11&amp;virtuemart_category_id[0]=2'">
...