**Steps to replicate the issue** (include links if applicable):
* On simplewiki, put this in your common.js file:
```lang=js
mw.loader.using(['mediawiki.util', 'jquery.ui', 'ext.gadget.morebits']).then(function() {
importScript('MediaWiki:Gadget-Twinkle.js');
});
```
* Refresh
**What happens?**:
* No browser devtools console message
**What should have happened instead?**:
* Browser devtools console message of some kind, such as "ResourceLoader: ext.gadget.morebits does not exist".
>>! In T346419#9733553, @Krinkle wrote:
> I'm tagging this as a task suitable for interested volunteers there.
>
> The objective is to update `mw.loader.using()`, which is defined in MediaWiki core's `mediawiki.base.js`, from jQuery.Deferred to instead use Promise.
>
> This approach solves the reported because the browsers naturally report uncaught promise rejections to the browser console.
>
> This approach avoids the problem described in T346419#9174761, because browsers //do not// report rejections for promises that have a catch handler.