[nicoburns]

I agree that the pattern of "services" is a good one. But you don't really need Angular's DI for this in javascript. You can just use an ES6 module.

[bradstewart]

Unless you care about the scope/lifecycle of the service. Or want to easily replace its implementation in different contexts (like tests).

[ng12]

Most test frameworks allow you to stub imports. DI is just one of the many wheels Angular has reinvented.