Make class auto inter return types from declaration file - node.js

Question

We are using a external package that doesn't have types, recreating it is too much overhaul.
We do know by trial and error the response of i.e (generateWallet) and want to make declarations for them instead of implementing each one.
What we currently have to do
Declaration file
interface ServiceClass {
generateWallet(): Wallet;
}
interface Wallet {
address: string;
privateKey: string;
}
Class
export class Service implements ServiceClass {
constructor() {}
generateWallet(): Wallet {
return externalPackage.generateWallet() // returns any;
}
// We dont want to do this for about hundred different functions
}
Wanted Output
import externalPackage from 'external-package';
const externalPackage.generateWallet(); // Shows return type as (Wallet)

Answer 1

You can add your own type description file for a package that does not have its own types.
Create package_name.d.ts file with a desired types like this:
/* eslint-disable camelcase */
declare module 'external-package' {
export interface Wallet {
address: string;
privateKey: string;
}
interface ExternalPackage {
generateWallet(): Wallet;
}
export default ExternalPackage;
}
Place this file into #types folder and add this folder to tsconfig.json:
{
"compilerOptions": {
... // other options
"typeRoots": [
"#types",
"node_modules/#types"
]
...
}