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.

Replacing or deleting bindings

Before an identifier is resolved, it is possible to replace or delete the binding of the identifier. This can be done by calling the replace or delete methods of the injector.