Follow button does not work most of the sometimes

I am using below code in my web app for twitter follow button:

<a href=https://twitter.com/ABHIJEEEEEEET class="twitter-follow-button"
data-show-count="true">Follow@directdialogs</a>
<script type="text/javascript" charset="utf-8">
window.twttr = (function (d,s,id) {
var t, js, fjs = d.getElementsByTagName(s)[0];
if (d.getElementById(id)) return; js=d.createElement(s); js.id=id;
js.src="//platform.twitter.com/widgets.js"; fjs.parentNode.insertBefore(js, fjs);
return window.twttr || (t = { _e: [], ready: function(f){ t._e.push(f) } });
}(document, "script", "twitter-wjs"));
</script>
<script>
twttr.ready(function (twttr) {
twttr.events.bind('follow', function(e) {
alert("FOLLOW!")
});
});
</script>
But alert("FOLLOW!") is not getting triggered in below cases:
1) Already logged out of twitter & not following @ABHIJEEEEEEET
2) Already logged out of twitter & following @ABHIJEEEEEEET
3) Already logged in to twitter & following @ABHIJEEEEEEET

Please help.