fix: support plugins that return an empty object (#15)

BREAKING CHANGE: `.plugin([plugin1, plugin2])` is now `.plugin(plugin1, plugin2)` (compare octokit/core.js#53, thanks @wolfy1339)

Author: gr2m

.github/workflows/build.yml

@@ -11,9 +11,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@master
-      - uses: actions/setup-node@v1
-        with:
-          node-version: 12
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v2
       - run: npm ci
       - run: npm run build

.github/workflows/release.yml

@@ -9,10 +9,8 @@ jobs:
     name: release
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@master
-      - uses: actions/setup-node@v1
-        with:
-          node-version: "12.x"
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v2
       - run: npm ci
       - run: npm run build
       - run: npx semantic-release

.github/workflows/test.yml

@@ -11,9 +11,7 @@ jobs:
   test:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@master
-      - uses: actions/setup-node@v1
-        with:
-          node-version: 12
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v2
       - run: npm ci
       - run: npm test

README.md

@@ -15,21 +15,21 @@ import { Base } from "javascript-plugin-architecture-with-typescript-definitions
 
 function myFooPlugin(instance: Base) {
   return {
-    foo: () => "foo"
+    foo: () => "foo",
   };
 }
 
 function myBarPlugin(instance: Base) {
   return {
-    bar: () => "bar"
+    bar: () => "bar",
   };
 }
 
 const FooTest = Base.plugin(myFooPlugin);
 const fooTest = new FooTest();
 fooTest.foo(); // has full TypeScript intellisense
 
-const FooBarTest = Base.plugin([myFooPlugin, myBarPlugin]);
+const FooBarTest = Base.plugin(myFooPlugin, myBarPlugin);
 const fooBarTest = new FooBarTest();
 fooBarTest.foo(); // has full TypeScript intellisense
 fooBarTest.bar(); // has full TypeScript intellisense

src/index.ts

@@ -13,9 +13,9 @@ type Constructor<T> = new (...args: any[]) => T;
  * @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
+type UnionToIntersection<Union> = (
+  Union extends any ? (argument: Union) => void : never
+) extends (argument: infer Intersection) => void // tslint:disable-line: no-unused
   ? Intersection
   : never;
 
@@ -31,16 +31,23 @@ export class Base {
   static plugins: TestPlugin[] = [];
   static plugin<
     S extends Constructor<any> & { plugins: any[] },
-    T extends TestPlugin | TestPlugin[]
-  >(this: S, plugin: T) {
+    T1 extends TestPlugin,
+    T2 extends TestPlugin[]
+  >(this: S, plugin1: T1, ...additionalPlugins: T2) {
     const currentPlugins = this.plugins;
+    let newPlugins: (TestPlugin | undefined)[] = [
+      plugin1,
+      ...additionalPlugins,
+    ];
 
     const BaseWithPlugins = class extends this {
-      static plugins = currentPlugins.concat(plugin);
+      static plugins = currentPlugins.concat(
+        newPlugins.filter((plugin) => !currentPlugins.includes(plugin))
+      );
     };
 
-    type Extension = ReturnTypeOf<T>;
-    return BaseWithPlugins as typeof BaseWithPlugins & Constructor<Extension>;
+    return BaseWithPlugins as typeof BaseWithPlugins &
+      Constructor<UnionToIntersection<ReturnTypeOf<T1> & ReturnTypeOf<T2>>>;
   }
 
   static defaults<S extends Constructor<any>>(this: S, defaults: Options) {
@@ -59,7 +66,7 @@ export class Base {
     // apply plugins
     // https://stackoverflow.com/a/16345172
     const classConstructor = this.constructor as typeof Base;
-    classConstructor.plugins.forEach(plugin => {
+    classConstructor.plugins.forEach((plugin) => {
       Object.assign(this, plugin(this, options));
     });
   }

test.ts

@@ -4,25 +4,38 @@ const fooPlugin = (test: Base) => {
   console.log("plugin evalutes");
 
   return {
-    foo: () => "foo"
+    foo: () => "foo",
   };
 };
 const barPlugin = (test: Base) => {
   console.log("plugin evalutes");
 
   return {
-    bar: () => "bar"
+    bar: () => "bar",
   };
 };
+const pluginWithEmptyObjectReturn = (test: Base) => {
+  return {};
+};
 
 describe("Base", () => {
   it(".plugin(fooPlugin)", () => {
     const FooTest = Base.plugin(fooPlugin);
     const fooTest = new FooTest();
     expect(fooTest.foo()).toEqual("foo");
   });
-  it(".plugin([fooPlugin, barPlugin])", () => {
-    const FooBarTest = Base.plugin([fooPlugin, barPlugin]);
+  it(".plugin(fooPlugin, barPlugin)", () => {
+    const FooBarTest = Base.plugin(fooPlugin, barPlugin);
+    const fooBarTest = new FooBarTest();
+    expect(fooBarTest.foo()).toEqual("foo");
+    expect(fooBarTest.bar()).toEqual("bar");
+  });
+  it(".plugin(fooPlugin, barPlugin, pluginWithVoidReturn)", () => {
+    const FooBarTest = Base.plugin(
+      fooPlugin,
+      barPlugin,
+      pluginWithEmptyObjectReturn
+    );
     const fooBarTest = new FooBarTest();
     expect(fooBarTest.foo()).toEqual("foo");
     expect(fooBarTest.bar()).toEqual("bar");
@@ -43,10 +56,10 @@ describe("Base", () => {
 
   it(".plugin().defaults()", () => {
     const BaseWithPluginAndDefaults = Base.plugin(fooPlugin).defaults({
-      baz: "daz"
+      baz: "daz",
     });
     const BaseWithDefaultsAndPlugin = Base.defaults({
-      baz: "daz"
+      baz: "daz",
     }).plugin(fooPlugin);
 
     const instance1 = new BaseWithPluginAndDefaults();