How Can I Reliably Determine if a Facebook User Has Liked My Page Using JavaScript?

Determining Facebook Page Affinity with JavaScript API

In the context of iFrame applications, the task of verifying whether a user has "liked" a particular Facebook page can be encountered. However, encountering inconsistencies while attempting to implement this functionality is not uncommon.

Consider the following code snippet:

FB.api({
    method:     "pages.isFan",
    page_id:        my_page_id,
},  function(response) {
        console.log(response);
        if(response){
            alert('You Likey');
        } else {
            alert('You not Likey :(');
        }
    }
);

Upon executing this code, it yields a puzzling result of "False" even though the user in question has indeed "liked" the associated page. The culprit behind this discrepancy lies in the need for an extended permission that has not been addressed.

Alternative Approach Using Signed Request

To circumvent this issue and reliably ascertain a user's "like" status, an alternative approach utilizing the signed request mechanism can be employed. By enabling the "OAuth 2.0 for Canvas" advanced option within Facebook, you can retrieve a signed request with every tab app request that contains crucial information about the user, including their "like" status:

function parsePageSignedRequest() {
    if (isset($_REQUEST['signed_request'])) {
      $encoded_sig = null;
      $payload = null;
      list($encoded_sig, $payload) = explode('.', $_REQUEST['signed_request'], 2);
      $sig = base64_decode(strtr($encoded_sig, '-_', '+/'));
      $data = json_decode(base64_decode(strtr($payload, '-_', '+/'), true));
      return $data;
    }
    return false;
  }
  if($signed_request = parsePageSignedRequest()) {
    if($signed_request->page->liked) {
      echo "This content is for Fans only!";
    } else {
      echo "Please click on the Like button to view this tab!";
    }
  }

This solution extracts the signed request, decodes it, and examines the "liked" property of the parsed JSON object to accurately determine the user's "like" status for your Facebook page.

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