Can the Angular $injector be decorated with $provide.decorator?

Question

Perhaps this is a terrible idea, but if it is then please tell me why and then pretend that it\'s an academic exercise that won\'t see the light of day in production.

Answer 1

The answer is: no.

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$provide.decorator is used to intercept service creation -- that is why it is called from .config block, when there is still time to configure all services, as none of them has been created. $provide.decorator basically gets the Provider of the service and swaps its $get with newly delivered decorFn.

$injector is not like other services. It is created, as the very first step of bootstrapping an application -- way before app.config is called. [look at functions: bootstrap and createInjector in angular source code]

But hey, you can achieve your goal quite easily by tweaking the source code just a bit :-) Particularly look at function invoke(fn, self, locals).

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UPDATE I got some inspiration from @KayakDave. You actually do not have to dig in the source-code itself. You can use the following pattern to observe each call to any of $injector methods:

 app.config(['$injector', function ($injector) {

      $injector.proper =
      {
          get : $injector.get,
          invoke : $injector.invoke,
          instantiate : $injector.instantiate,
          annotate : $injector.annotate,
          has : $injector.has
      }

      function getDecorator(serviceName)
      {
          console.log("injector GET: ", serviceName);
          return this.proper.get(serviceName);
      }

      function invokeDecorator(fn, self, locals)
      {
          console.log("injector INVOKE: ", fn, self, locals);
          return this.proper.invoke(fn, self, locals);
      }

      function instantiateDecorator(Type, locals)
      {
          console.log("injector INSTANTIATE: ", Type, locals);
          return this.proper.instantiate(Type, locals);
      }

      function annotateDecorator (fn)
      {
          console.log("injector ANNOTATE: ", fn);
          return this.proper.annotate(fn);
      }

      function hasDecorator(name)
      {
          console.log("injector HAS: ", name);
          return this.proper.has(name);
      }

      $injector.get = getDecorator;
      $injector.invoke = invokeDecorator;
      $injector.instantiate = instantiateDecorator;
      $injector.annotate = annotateDecorator;
      $injector.has = hasDecorator;
  }]);

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PLNKR