在'root'，'platform'，'any' w.r.t providedIn 中，在 Angular 的这种情况下应该首选哪一个？

Question

Out of 'root', 'platform', 'any' w.r.t providedIn, which one should be preferred in which case in Angular?

https://angular.io/api/core/Injectable

'root' : The application-level injector in most apps.
'platform' : A special singleton platform injector shared by all applications on the page.
'any' : Provides a unique instance in every module (including lazy modules) that injects the token.

In which kind of cases would we want unique instance in every module rather than letting the root deal with all?

What is an example use case of platform?

Answer 1

So, while not sure I can tailor this answer to any specific use case, my initial impression of the new options here is that they aren't tremendously useful except in edge cases where the developer isn't properly using Angular. Based on a quick read through of some articles, including this one and this one , it appears that the new options give the developer some added flexibility to misdesign their application and introduce strange and difficult-to-track bugs.

Angular's DI framework allows you to define the scope for your services (remember that services are where your application's state lives ). The option 'root' declares that only one instance of your service will be created for the whole application, so the whole application will share whatever state the service holds. The alternative was to specify a specific module in the providedIn choice or, more commonly, to specify a provides: section of your module declaration. In that case, you either need to import your service by importing a module, or you need to explicitly declare that it is contained within one module.

The key with the old approach is that, if you messed it up, you would get an easy-to-track error at runtime.

The new approach allows you to specify a bit more ambiguity. 'any' means what it says - every module needing a particular service will generate its own. This will almost certainly trip up beginning and intermediate level developers, who are not familiar with the symptoms of inconsistent state in their programs. Conversely, 'platform' will allow multiple applications loaded into the same window (does this include applications in different iFrames?) to share the same state. At best, this option is unnecessary (only one Angular application should ever be loaded at a time, unless you're talking about Angular Elements ), and at worst, it runs the risk of making your application difficult or impossible to test.

Bottom line: you shouldn't find yourself using these new choices, unless you made a pretty big mistake earlier in your architecture process, or you're writing a library of some sort.