Improve the return type of cloudinary.v2.config() in TypeScript (#494)

* Improve the return type of cloudinary.v2.config()

  - The original typescript definition was to return void, but the
    actual code always returns something, either the config or a property.
  - Calls will generally return the ConfigOptions

    const config = cloudinary.v2.config()

  - A string parameter works like a getter, returning the property

    cloudinary.v2.config("private_cdn") === true

  - Two parameters acts like a setter, but returns the config object

    const config = cloudinary.v2.config("private_cdn", true)

  - If the function gets two parameters, but the 2nd is undefined, it
    acts like the getter instead of setting the config key to undefined

    cloudinary.v2.config("private_cdn", undefined) === true

Author: MrLeebo

types/cloudinary_ts_spec.ts

@@ -1,16 +1,41 @@
 import * as cloudinary from 'cloudinary';
 import * as Http from "http";
 
-// $ExpectType void
-cloudinary.v2.config({
-    cloud_name: 'demo',
-});
+// $ExpectType ConfigOptions
+cloudinary.v2.config();
 
-// $ExpectType void
+// $ExpectType ConfigOptions
 cloudinary.v2.config(true);
 
-// $ExpectType void
-cloudinary.v2.config("private_cdn", true);
+// $ExpectType ConfigOptions
+cloudinary.v2.config({ cloud_name: "demo" });
+
+// $ExpectError
+cloudinary.v2.config({ cloud_name: 0 });
+
+// $ExpectType boolean | undefined
+cloudinary.v2.config("private_cdn");
+
+// $ExpectType string | undefined
+cloudinary.v2.config("cloud_name", undefined);
+
+// $ExpectType any
+cloudinary.v2.config("not_a_key");
+
+// $ExpectType boolean | undefined
+cloudinary.v2.config(true).private_cdn;
+
+// $ExpectType boolean
+cloudinary.v2.config("private_cdn", true).private_cdn;
+
+// $ExpectType string | undefined
+cloudinary.v2.config(true).cloud_name;
+
+// $ExpectType string
+cloudinary.v2.config("cloud_name", "foo").cloud_name;
+
+// $ExpectError
+cloudinary.v2.config("private_cdn", true, "extra_parameter");
 
 // $ExpectType string
 const test = cloudinary.v2.image("front_face.png", {

types/index.d.ts

@@ -686,9 +686,11 @@ declare module 'cloudinary' {
 
         function cloudinary_js_config(): string;
 
-        function config(new_config: ConfigOptions | string, new_value?: string | boolean): void;
+        function config(new_config?: boolean | ConfigOptions): ConfigOptions;
 
-        function config(new_config: boolean | object): void;
+        function config<K extends keyof ConfigOptions, V extends ConfigOptions[K]>(key: K, value?: undefined): V;
+
+        function config<K extends keyof ConfigOptions, V extends ConfigOptions[K]>(key: K, value: V): ConfigOptions & { [Property in K]: V }
 
         function url(public_id: string, options?: TransformationOptions | ConfigAndUrlOptions): string;