window.fbAsyncInit = function() {
  FB.init({
    appId      : 'My App ID',
    cookie     : true,
    xfbml      : true
  });
  FB.getLoginStatus(function(response) {
    alert(response.status);
    if (response.status === 'connected') {
      var uid = response.authResponse.userID;
      var accessToken = response.authResponse.accessToken;
      alert(uid);
    }
    else{
        window.location.href="URL where i'm redirecting my app after logged out from facebook";
    }
  });
};

(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 = "https://connect.facebook.net/en_US/sdk.js";
  fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));