Google plus button, you can set a callback attribute to a js function,
<g:plusone href="http://youtubeplaylist.net" callback="plusClick"></g:plusone>
In the callback js function, you can check the state, if they have clicked +1 or removed +1.
function plusClick(data) {
if (data.state == "on") {
alert("+1");
// +1
} else if (data.state == "off") {
// -1 (user took their +1 Away)
alert("-1");
}
}
(function () {
var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true;
po.src = 'https://apis.google.com/js/plusone.js';
var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s);
})();
There are some other js callback as well, such as onstartinteraction (when the +1 dialog popups up), onendinteraction (when +1 dialog close).
For more information, check out this google page, https://developers.google.com/+/plugins/share/#sharetag-parameters
