How to Ensure Library B Uses the Same Version of Library C as My App

[maliknajjar]

Hello,

I have a scenario where my application imports Library B, and both my app and Library B rely on Library C. I want to ensure that Library B uses the same version of Library C as my application.

How can I enforce this in Deno?

[marvinhagemeister]

This is solved by both libraries specifying a version range instead of an exact version. Example:

• lib-b depends on lib-c@^1.0.0 (note the ^ character)
• your app depends on lib-c@^1.1.0 (again, note the ^ character)

This will install lib-c only once and both your app and lib-b will share the exact same version. This will always be the case for as long as the version ranges match. A scenario where they would not match would be where your app depends on lib-c@^3.0.0 but lib-b depends on lib-c@^1.0.0. No version of lib-c can satisfy both version constraints, so you'll end up with two copies.

To see all available version constraint characters, check out this page in the docs. Note that version specifiers only work with jsr: and npm: imports and not with http: or https:.

In the Node ecosystem you'll come across the term peerDependencies quite a bit which is kinda the same as version constraint, with the additional feature that package managers print a big warning or error when the version ranges don't match. Deno supports this, when you're defining your dependencies in package.json as well. That said for Deno first projects that is usually not needed and specifying correct version ranges is enough.

[maliknajjar]

hi @marvinhagemeister. thanks for responding

the issue with the current way is that because deno doesn't throw an error on mismatching versions. deno will end up downloading a different versions of the C library for the B library without the user even noticing it. he will do it in a silent way. no errors not even showing a warning. and this behavior can cause unexpected behavior and bugs. I actually had a bug because deno made library B use a different version of library C than the main app uses
I'm building a framework. so I have multiple libraries that are used together
and if I the author of the libraries didn't notice deno using another version of C library imagine the normal user
I can fix this now by matching the versions. but what if a user of the framework will upgrade the core app and forgets to upgrade the B library. a mismatch will happened an it will cause a lot of unexpected behavior. that's why I suggest to have the peerDependancy in the deno.json also. so that it will at least tell the user that there is a mismatch. and since peerDependancy is already implemented in deno for package.json it should be easily added in deno.json too. (Im not sure. but I think so)

[marvinhagemeister]

Right, that info that you're asking for peer dependencies explicitly was missing in your original post. There is an issue for native peerDependencies support in Deno here #26199

[maliknajjar]

yes Im the creator of that issue 🥲

[maliknajjar]

but they tagged it as a question. not as a feature request

[marvinhagemeister]

Right, I changed the tags to match.