If you do go with TypeScript have a look at Nx. It's tooling around TypeScript monorepo that helps you do exactly what you want: write code once and share it between backend/multiple frontends. It suppports Express or NestJS in the backend and Angular, React, Web Components in the Frontend. https://nx.dev/

If you want to make it work with Ionic/NativeScript/Electron as well use xplat. https://github.com/nstudio/xplat