Javascript function that waits for an object to be available, and then invokes with callback

when_available.js

function whenAvailable(name, callback) {
  var interval = 10;
  window.setTimeout(function() {
    if(window[name]) {
      callback(window[name]);
    } else {
      setTimeout(arguments.callee, interval);
    }
  }, interval);
}

//Sample usage: Facebook JS SDK
whenAvailable('FB',function(fb) {
  fb.api(/*Some Facebook API call*/);
});