Tumblr为共享按钮生成以下代码。如何在积极采取行动时捕获回调？
<!-- Put this tag wherever you want your button to appear -->
<span id="tumblr_button_abc123"></span>
<!-- Set these variables wherever convenient -->
<script type="text/javascript">
var tumblr_link_url = "http://www.example.com/permalink/my-article";
var tumblr_link_name = "My Awesome Article";
var tumblr_link_description = "Lorem ipsum...";
</script>
<!-- Put this code at the bottom of your page -->
<script type="text/javascript">
var tumblr_button = document.createElement("a");
tumblr_button.setAttribute("href", "http://www.tumblr.com/share/link?url=" + encodeURIComponent(tumblr_link_url) + "&name=" + encodeURIComponent(tumblr_link_name) + "&description=" + encodeURIComponent(tumblr_link_description));
tumblr_button.setAttribute("title", "Share on Tumblr");
tumblr_button.setAttribute("style", "display:inline-block; text-indent:-9999px; overflow:hidden; width:81px; height:20px; background:url('http://platform.tumblr.com/v1/share_1.png') top left no-repeat transparent;");
tumblr_button.innerHTML = "Share on Tumblr";
document.getElementById("tumblr_button_abc123").appendChild(tumblr_button);
</script>