feat: full TypeScript support for plugin API

gr2m · gr2m · commit 3f06e0e1ba8d · 2019-11-03T08:48:07.000-08:00
diff --git a/src/index.ts b/src/index.ts
@@ -3,10 +3,18 @@ import { Collection, HookCollection } from "before-after-hook";
 import { request } from "@octokit/request";
 import { graphql, withCustomRequest } from "@octokit/graphql";
 
-import { OctokitOptions, Plugin, RequestParameters } from "./types";
+import {
+  Constructor,
+  OctokitOptions,
+  OctokitPlugin,
+  RequestParameters,
+  ReturnTypeOf
+} from "./types";
 import { VERSION } from "./version";
 import { withAuthorizationPrefix } from "./auth";
 
+export { OctokitOptions } from "./types";
+
 export class Octokit {
   static defaults(defaults: OctokitOptions) {
     return class OctokitWithDefaults extends this {
@@ -20,16 +28,20 @@ export class Octokit {
     };
   }
 
-  static plugins: Plugin[] = [];
-  static plugin(plugins: Plugin | Plugin[]) {
+  static plugins: OctokitPlugin[] = [];
+  static plugin<T extends OctokitPlugin | OctokitPlugin[]>(pluginOrPlugins: T) {
     const currentPlugins = this.plugins;
-    const newPlugins = Array.isArray(plugins) ? plugins : [plugins];
+    const newPlugins = Array.isArray(pluginOrPlugins)
+      ? pluginOrPlugins
+      : [pluginOrPlugins];
 
-    return class NewOctokit extends this {
+    const NewOctokit = class extends this {
       static plugins = currentPlugins.concat(
         newPlugins.filter(plugin => !currentPlugins.includes(plugin))
       );
     };
+
+    return NewOctokit as typeof NewOctokit & Constructor<ReturnTypeOf<T>>;
   }
 
   constructor(options: OctokitOptions = {}) {
@@ -93,7 +105,9 @@ export class Octokit {
     // apply plugins
     // https://stackoverflow.com/a/16345172
     const classConstructor = this.constructor as typeof Octokit;
-    classConstructor.plugins.forEach(plugin => plugin(this, options));
+    classConstructor.plugins.forEach(plugin => {
+      Object.assign(this, plugin(this, options));
+    });
   }
 
   // assigned during constructor
@@ -107,7 +121,4 @@ export class Octokit {
     [key: string]: any;
   };
   hook: HookCollection;
-
-  // allow for plugins to extend the Octokit instance
-  [key: string]: any;
 }
diff --git a/src/types.ts b/src/types.ts
@@ -11,4 +11,29 @@ export type OctokitOptions = {
   [option: string]: any;
 };
 
-export type Plugin = (octokit: Octokit, options: OctokitOptions) => void;
+export type Constructor<T> = new (...args: any[]) => T;
+
+export type ReturnTypeOf<
+  T extends AnyFunction | AnyFunction[]
+> = T extends AnyFunction
+  ? ReturnType<T>
+  : T extends AnyFunction[]
+  ? UnionToIntersection<ReturnType<T[number]>>
+  : never;
+
+/**
+ * @author https://stackoverflow.com/users/2887218/jcalz
+ * @see https://stackoverflow.com/a/50375286/10325032
+ */
+type UnionToIntersection<Union> = (Union extends any
+  ? (argument: Union) => void
+  : never) extends (argument: infer Intersection) => void // tslint:disable-line: no-unused
+  ? Intersection
+  : never;
+
+type AnyFunction = (...args: any) => any;
+
+export type OctokitPlugin = (
+  octokit: Octokit,
+  options: OctokitOptions
+) => { [key: string]: any } | void;
