Function overloading in index.d.ts file

Question

Solved: restarting VS code helped :blush:

I have a module written in es6 (not typescript) and I want to add ts declaration file to it. Module export only one function which can be called like this:

fn(A, C)
fn(A, B, C)

Here is declaration file I have for now:

/// <reference types="node" />
/// <reference types="graphql" />

declare module 'graphql-add-middleware' {

  type middlewareFn = (root: any, args: any, context: any, info: any, next: () => Promise<any>) => Promise<any>;

  export function addMiddleware (
    schema: GraphQLSchema,
    fn: middlewareFn,
  ): void;

  export function addMiddleware (
    schema: GraphQLSchema,
    path: string,
    fn: middlewareFn,
  ): void;
};

I thought that typescript will detect two variations of this function (2 or 3 args) but in a project where I am using this module ts complains if I try to addMiddleware(schema, fn). It says that 3 args were exepcted. It does not complain if I do addMiddleware(schema, path, fn).

What is wrong with my declaration file? How I can make it work?

Update - see screen below what VS code says:

Edit: you can test it by yourself - this is the package, it's published to npm: https://github.com/alekbarszczewski/graphql-add-middleware

Answer 1

I know the OP said it's solved by a VS code restart, but it didn't for me. Here's the solution that worked.

1. Define each function interface as a type
2. Combine the types in the actual function declaration

In your *.d.ts

type FnOverload1 = (a: string) => void;
type FnOverload2 = (a: string, b: string) => void;
type FnOverload3 = (a: string, b: string, c: string) => void;

type Fn = FnOverload1 & FnOverload2 & FnOverload3

Using Fn("a"), Fn("a", "b") or Fn("a", "b", "c") no longer raises a warning or error in the IDE.