I have added a javascript function am  trying to the url of the main product image in the ProductMain.ascx template ..\Portals\0\SmithCart\Templates.
But whenever I call it from another event or function on the page it always returns null.  Is this the correct way to do it? Or is there a better way?

<script type="text/javascript">
function getImageUrl() {
        var imagesLength = document.images.length;
        var url = document.getElementById("<%=myMainImage.ClientID%>").value;
        return url;
    }</script>

I am using DNN 7.0.6 and Smith Cart 5.52.
What I was trying to do is dynamically add a Pinterest button because the Show Share bar (configured on the Product Details page) doesn't have it. It only has Twitter, Google plus, and Facebook.

Also, the advertised Smith Social Media Sharebar doesn't list Pinterest as an option.