What does @firebase/[email protected] do and when should I use it?

Question

On the phase where yarn is linking its dependencies I get the following block of warnings:

warning "firebase > @firebase/[email protected]" has unmet peer dependency "@firebase/[email protected]".  
warning "firebase > @firebase/[email protected]" has unmet peer dependency "@firebase/[email protected]".  
warning "firebase > @firebase/[email protected]" has unmet peer dependency "@firebase/[email protected]".
...

some more unment peer dependency warnings about "@firebase/[email protected]" from different firebase packages I removed here for the sake of better readability.

...  
warning " > [email protected]" has unmet peer dependency "dom-tools@^0.1.1".  
warning " > [email protected]" has unmet peer dependency "wolfy87-eventemitter@^4.3.0".  

Even though I did read The docs about dependency types, I still do not understand:

1) What are peer dependencies? [now I do... please read edit below]
2) Why and how are they used? [now I do... please read edit below]

This lack of understanding also leads to me being uncertain about what I should do about those warnings provided by yarn.

3) Should I add @firebase/[email protected], dom-tools@^0.1.1 and wolfy87-eventemitter@^4.3.0 as dependencies?
4) if so then should those be normal or dev dependencies?

Edit:
It was suggested that this is a duplicate of Why use peer dependencies in npm for plugins? so I went and read it. I now understand better what peer dependencies are in general and I do recommend everyone reaching this Q that does no understand what peer dependencies are to go ahead and read said Question and answer provided there.

Never the less, I still don't know how to resolve said warning and Q's 3 and 4 are still let unanswered for me.

I do understand that @firebase/[email protected] expects me to somhow use that code in @firebase/[email protected] when communicating with it... but I do not knwo where, when am I how I am expected to do so.

The fact that I don't use it could mean that its something optional that I don't actually need and this makes it "an implementation detail" (to use language from https://stackoverflow.com/a/34645112/25412 ) or that I am missing something in how I am using @firebase/[email protected].

I am not asking about the peer dependencies of plotjs because plotjs is not something that I am using directly to begin with so I am guessin the first option of an optional "implementation detail" applies here (at least for now).

So maybe someone can provide more insight into what @firebase/[email protected] does and how and when it can/should be used?

Answer 1

According to one of the collaborators maintaining the firebase javascript sdk, this warning is generated by a known bug in yarn. See this related issue in the firebase-js-sdk:

After a quick google search, It appears to be a known issue with yarn. If a peer dependency is installed by a dependency's dependency (I know it's a mouthful), yarn will complain about it. Your product is totally safe, there is nothing to worry about. You can also use npm install instead, and there is no warning.

In conclusion: ignore the "@firebase/..." has unmet peer dependency "@firebase/[email protected]". warnings.