Extension subjects can be declared using declare, and are used in one of two modes:

1. To load a singleton from a graph subject having a property http://js.m-ld.org/#require. In this case a SingletonExtensionSubject (or a subclass) should be instantiated directly using {@link OrmUpdating#get}, and the singleton object obtained with singleton, e.g. with data:

   {
    "@id": "myCustomSingleton",
    "http://js.m-ld.org/#require": "my-custom-module",
    "http://js.m-ld.org/#class": "MyExtClass"
   }
   

   The single custom instance for this class might be loaded with:

   const extType = orm.get('myCustomSingleton',
    src => new SingletonExtensionSubject<MyExtType>({ src, orm });
   const ext: MyExtType = extType.singleton;
   

2. To load an instance from a graph subject that itself has the property type http://js.m-ld.org/#require. This indirection allows for many graph subjects to have custom type without re-declaring the module & export. The instance method is provided to load the instance, e.g. with data:

   {
    "@id": "myCustomInstance",
    "@type": {
      "@id": "myCustomClass",
      "http://js.m-ld.org/#require": "my-custom-module",
      "http://js.m-ld.org/#class": "MyExtClass"
    }
   }
   

   A custom instance for this class might be loaded with:

   const ext: MyExtType = orm.get('myCustomInstance',
    src => ExtensionSubject.instance<MyExtType>({ src, orm });
   

experimental