Load Facebook SDK for JavaScript

LoadFacebook.js

<script>
    window.fbAsyncInit = function() {
        FB.init({
            appId    :    'your facebook app id',
            xfbml    :    true,
            version:    'v2.6'
        });
    };
    (function(d, s, id) {
        var js, fjs = d.getElementsByTagName(s) [0];
        if (d.getElementById(id)) {return;}
        js = d.createElement(s); js.id = id;
        js.src = "//connect.facebook.net/en_US/sdk.js";
        fjs.parentNode.insertBefore(js, fjs);
    } (document, 'script', 'facebook-jssdk'));
</script>