What is a replacement for FB.ensureInit() now?

I am loading FB API in asynchronous way:

<div id="fb-root"></div>
<script>
  window.fbAsyncInit = function() {
    FB.init({appId: 'your app id', status: true, cookie: true,
             xfbml: true});
  };
  (function() {开发者_JAVA百科
    var e = document.createElement('script'); e.async = true;
    e.src = document.location.protocol +
      '//connect.facebook.net/en_US/all.js';
    document.getElementById('fb-root').appendChild(e);
  }());
</script>

How do I know when it is initialized? What is the replacement for FB.ensureInit() method that would prevent running enclosed code until API is initialized?

1° When you load Facebook's script it will execute window.fbAsyncInit, that you already have in your script. If you include a method call as the last row, inside that method you can be sure FB has been initialized.

The code above becomes

window.fbAsyncInit = function() {
  FB.init({appId: 'your app id', status: true, cookie: true,
           xfbml: true});
  afterInit();
};

2° You can also define your own fbEnsureInit that works as previously and use a semaphore instead of a method call: (Originally from another answer.)

window.fbAsyncInit = function() {
  FB.init({appId: 'your app id', status: true, cookie: true,
           xfbml: true});
  fbApiInitialized = true;
};

function fbEnsureInit(callback) {
    if (!window.fbApiInitialized) {
        setTimeout(function() { fbEnsureInit(callback); }, 50);
    } else {
        if (callback) { callback(); }
    }
}

3° Yet another way is described in Performance tips for Connect wiki. This approach inspects the state of the script and does a callback when the script is loaded.

So, in your code above, before appending the script insert the following code:

script.onload = script.onreadystatechange = function() {
  if ( !done && (!this.readyState || this.readyState == "loaded" ||
       this.readyState == "complete") ) {
    done = true;
    afterInit();
  }
};

The method afterInit will be called when the script is loaded.