webqr.com is actually an implementation of https://github.com/LazarSoft/jsqrcode which @rapropos also posted. So you can probably use this in your app.
There are multiple Angular versions of jsqrcode out there, unfortunately all I could find are for AngularJS and so for Ionic 1:
But I’m sure you can adapt these or if you search a bit more one for Angular will turn up.