javascript - How to workaround 'FB is not defined'?

Question

Sometimes I'm getting the "FB is not defined" issue when loading the http://connect.facebook.net/en_US/all.js

I've realized that the problem is because sometimes my website just doesn't load that file. So it gets nothing, and the object FB literally doesn't exist.

My solution is to prevent my users when this happens, so I've tried the following codes in JavaScript but none seems to work:

if (FB) {/*run the app*/} else {/*alert the user*/}
if (FB!==false) {/*run the app*/} else {/*alert the user*/}
if (FB!='undefined') {/*run the app*/} else {/*alert the user*/}

thanks for the answer!

Answer 1

I think you should solve the main issue instead, which solution is provided by Facebook (Loading the SDK Asynchronously):

You should insert it directly after the opening tag on each page you want to load it:

<script>
  window.fbAsyncInit = function() {
    FB.init({
      appId      : 'your-app-id',
      xfbml      : true,
      version    : 'v2.1'
    });
  };

  (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>

From the documentation:

The Facebook SDK for JavaScript doesn't have any standalone files that need to be downloaded or installed, instead you simply need to include a short piece of regular JavaScript in your HTML that will asynchronously load the SDK into your pages. The async load means that it does not block loading other elements of your page.

UPDATE: using the latest code from the documentation.