YT.ready is not a function

I'm using `angular-youtube-embed` in an es6 webpack angular project. I'm loading the youtube iframe API from a file `youtubeapi.js`, followed by `import ./youtubeapi` in `index.js` where the angular module declaration is made:

```
import './youtubeapi';
import angular-youtube-embed from 'angular-youtube-embed';

angular.module('videoApp', [angular-youtube-embed]);
```

When navigating to a page which uses `videoApp`, I get the error `YT.ready is not a function`.

On refreshing the page, the error goes away. I'm wondering how to make sure the youtube API has loaded before `angular-youtube-embed` directives are run?