Writing declaration.d.ts for JavaScript modules, and Extending incomplete @types modules

If you have used TypeScript long enough, you should realize that you can create declaration.d.ts with declare module 'javascript-module' for untyped JavaScript modules.

However, you can go far beyond that. Indeed, the best way, if you have time, is to contribute to https://github.com/DefinitelyTyped/DefinitelyTyped. However, the process is slow, and can take around 1 week for @types repo to get updated.

I realized that you can do beyond declare module 'javascript-module'; by

declare module 'javascript-module' {
   export = JavaScriptModule;

   class JavaScriptModule {
   }

   namespace JavaScriptModule {
        interface IBlahBlah {}
   }
}

Now, the typing is in your control.

Also, if @types/javascript-module is insufficient, you can do this,

import JavaScriptModule from "javascript-module";

declare module "javascript-module" {
    interface JavaScriptModule {
        additionalMethod: () => void;
    }

    namespace JavaScriptModule {
        interface IBlahBlahBlah {}
   }
}

JavaScriptModule.prototype.additionalMethod = function() {
    this...
}

After all, what I want to say is that you can extend TypeScript.

Good luck exploring.