From “Web Development with Bootstrap 4 and Angular 2 – Second Edition”

In one moment of compilation, a TypeScript compiler can generate a declaration file which contains only signatures of the exported types. The resulting declaration file with the extension .d.ts along with a JavaScript library or module can be consumed later by a third-party developer. You can find a vast collection of declaration files for many popular JavaScript libraries at:

• The DefinitelyTyped (https://github.com/DefinitelyTyped/DefinitelyTyped)
• The Typings registry (https://github.com/typings/registry)

I’m so glad I bought this ebook. No DRM and this little gem to help me implement an actually usable Eiffel to JavaScript/WebAssembly compiler where with “actually usable” it means coming with batteries, i.e. binding for foreign libraries. Without them any effort is doomed.