Basic DI with typescript

basic_di.ts

Symbol.metadata ??= Symbol("metadata");

// base
type ContainerItemKinds = "class" | "value";
type ContainerKey = symbol | string | number;
type ContainerItem = { obj: unknown, kind: ContainerItemKinds };
const container = new Map<ContainerKey, ContainerItem>();

const inject = (key: ContainerKey, value: unknown, kind: ContainerItemKinds = "value") => {
  container.set(key, { obj: value, kind: kind });
}

// decorator
function injectable(key?: ContainerKey) {
  return (source: any, context: ClassMethodDecoratorContext) => {
    if (context.kind === "class") {
      const name = key ?? context.name;

      inject(name, source, "class");
    }
  };
}

function di(strings: TemplateStringsArray) {
  const name = strings[0];
  const item = container.get(name);
  
  if (item === undefined) {
    return undefined;
  }

  if (item.kind === "class") {
    const Type = item.obj as { new (): any };
    return new Type();
  }

  return item.obj;
}

@injectable()
class C {
}

@injectable("d")
class D {
}

const c = new C();

console.log(di`C`);