How to use regular 3rd party js libs with Jhipster 4?

I'm using Jhipster 4 with Angular 2 and need to use a 3rd party lib in my project, however the library is no on npm and doesn't have an .d.ts file. I need to include directly the js. Import inside vendor.ts works for libraries installed via npm but won't work with my js, how can I use this file in my project?