feat: allow to type available services

README.md

@@ -216,6 +216,38 @@ const injector = new Injector([
 ```
 
 
+### Type Service Retrival
+
+[`didi`](https://github.com/nikku/didi) ships type declarations that allow you to use it in a type safe manner.
+
+#### Explicit Typing
+
+Pass a type attribute to `Injector#get` to retrieve a service as a known type:
+
+```typescript
+const hifiComponent = injector.get<HifiComponent>('hifiComponent');
+
+// typed as <HifiComponent>
+hifiComponent.toggle();
+```
+
+#### Implicit Typing
+
+Configure the `Injector` through a service map and automatically cast services
+to known types:
+
+```typescript
+type ServiceMap = {
+  'hifiComponent': HifiComponent
+};
+
+const injector = new Injector<ServiceMap>(...);
+
+const hifiComponent = injector.get('hifiComponent');
+// typed as <HifiComponent>
+```
+
+
 ## Credits
 
 This library builds on top of the (now unmaintained) [node-di][node-di] library. `didi` is a maintained fork that adds support for ES6, the minification safe array notation, and other features.

lib/index.d.ts

@@ -71,13 +71,21 @@ export type LocalsMap = {
 
 export type ModuleDefinition = ModuleDeclaration;
 
-export class Injector {
+
+export class Injector<
+  ServiceMap = null
+> {
 
   /**
    * Create an injector from a set of modules.
    */
   constructor(modules: ModuleDefinition[], parent?: InjectorContext);
 
+  /**
+   * Return a named service, looked up from the existing service map.
+   */
+  get<Name extends keyof ServiceMap>(name: Name): ServiceMap[Name];
+
   /**
    * Return a named service, and throws if it is not found.
    */

test/integration/ts.spec.ts

@@ -59,6 +59,39 @@ describe('typed', function() {
       expect(injector).to.exist;
     });
 
+
+    it('should offer typed injections', function() {
+
+      // given
+      type ServiceMap = {
+        'foo': 1,
+        'bar': 'BAR'
+      };
+
+      // when
+      const injector = new Injector<ServiceMap>([
+        {
+          foo: [ 'value', 1 ],
+          bar: [ 'value', 'BAR' ]
+        }
+      ]);
+
+      // then
+      const foo = injector.get('foo');
+      expect(foo).to.eql(1);
+
+      const bar = injector.get('bar');
+      expect(bar).to.eql('BAR');
+
+      const baz = injector.get('baz', false);
+      expect(baz).not.to.exist;
+
+      // illegal usage, but if you think you know better
+      // we still accept it
+      const boolBar = injector.get<boolean>('bar');
+      expect(boolBar).to.exist;
+    });
+
   });