Binding

After declaring identifiers and dependencies, it is necessary to establish a binding relationship between the identifiers and dependencies, and register these bindings in the injector. The injector can only return dependencies based on identifiers when it knows a set of bindings.

There are two ways to register bindings on the injector:

• As parameters of the injector constructor
• By calling the add method of the injector

As parameters of the injector constructor

The first parameter of the Injector constructor is a set of bindings. You have seen a lot of code like this in the previous section:

const injector = new Injector([
  [SomeClass],
  [IdentifierA, { useClass: SomeClass }],
  [IdentifierB, { useValue: SomeValue }],
  [IdentifierC, { useFactory: SomeFactory }],
  [IdentifierD, { useAsync: SomeAsyncFunction }],
]);

By calling the add method of the injector

injector.add([SomeClass]);
injector.add([IdentifierA, { useClass: SomeClass }]);
injector.add([IdentifierB, { useValue: SomeValue }]);

This approach is more flexible because it does not restrict when you can register bindings. However, this type of binding can be a double-edged sword as it may not have been registered by the time you retrieve dependencies through the injector. Therefore, we recommend using the first method as a priority unless you can ensure the correct order of registration and retrieval.