Use external javascript library

Ionic Framework ionic-v3
1

Hello

I’d like to implement a external javascript library (alphaTab). How do I do this in typescript/IONIC?
Is there somebody who could help me with this? I imported the directory in the assets folder. But I can’t seem to import it in typescript. I get the error message: 'TS2306: File ‘AlphaTab.js’ is not a module etc.

Thanks in advance!