Question

I need using javascript to check if the current user is fan of my page.

I goto here https://developers.facebook.com/docs/reference/rest/pages.isFan/. In Test Console I don’t understand about Application parameter?

I using this code below, but it’s always alert “You like the Application” for any user even guest

window.checkDoesLike = function() {
  FB.api({ method: 'pages.isFan', page_id: '138992766181857' }, function(resp) {
    if (resp) {
      alert('You like the Application.');
    } else {
      alert("You don't like the Application.");
    }
  });
};

Answer 1

I’ve written an extended tutorial about this here.

There are a couple of points to highlight:

1. You are missing the uid parameter
2. using if(resp) is not enough

Better code:

FB.api({ method: 'pages.isFan', page_id: 'page_id_here', uid: 'user_id_here' }, function(resp) {
    if (resp == true) {
      alert('user_id likes the Application.');
    } else if(resp.error_code) {
      alert(resp.error_msg);
    } else {
      alert("user_id doesn't like the Application.");
    }
});

Quoting:

Once again, you need to check the response of the call if true or
not…using if(resp) is NOT enough! The example in the Facebook
JavaScript Test Console is a bit misleading (the does-like example),
since if you don’t grant the user_likes permission and just try it
with uid: ‘579187141’ it would result that the user likes the
application which is not true!
P.S: I just decremented my user id to get the above user which (it
seems) he has a strict privacy for pages he likes!