Personally, I would rather start with the v3 ecosystem knowing there's a risk we may have to migrate backwards to v2. The alternative is to go with v2 and know for sure that we have to migrate up to v3.

When googling "is Vue 3 production ready" this single forum post (which is clearly the definitive source of truth) says "no". But will Vue 3 be production ready by the time we want to deploy the search widget? Hopefully!

Regardless, my thinking on this decision rests primarily on one question:

What version is or will be available in Core?

And as of February 6th 2020, that's Vue 2.6.11.

(sidenote) as of April 15th we also have Vuex! https://gerrit.wikimedia.org/r/#/c/mediawiki/core/+/583818/

@Catrope, can the Vue 3 beta be made available in Core (maybe as a vue-next module)? If not now, what do you think the timeline would be?

In T249725#6075279, @Niedzielski wrote:

@Catrope, can the Vue 3 beta be made available in Core (maybe as a vue-next module)? If not now, what do you think the timeline would be?

I don't think we should make a non-production-ready version of Vue available in MW core. I also don't think making multiple versions of Vue available would be helpful, probably not even in a migration context. It would be way too easy to end up loading both versions of Vue on the same page (to support some Vue 2 features and some Vue 3 features), and any shared code (like component libraries) would either depend on one version of the other, or have to be forked so that there's a Vue 2 and Vue 3 version of them (at least for dependency management purposes; the actual code may or may not be very different).

Migrating from Vue 2 to Vue 3 will likely not be a big change for most code, it'll just add features. The things being deprecated/removed are obscure things, for the most part. The initialization code will change, which I think is going to be the hardest part to deal with, but we could wrap that with a compatibility wrapper, or advocate for the Vue 3 compat build to support both calling styles. For everything else, I'm hoping we'll be able to have a smooth migration using the compat build. Additionally, most new features in Vue 3 are available as plugins for Vue 2, and we could start using those before we upgrade.

Here's an example of what a Vue 2 -> Vue 3 migration looks like. I'll file a task for pre-planning the migration so that we can get ahead of some of those changes, and minimize the amount of work we need to do in the future.

Thanks, @Catrope!

Additionally, most new features in Vue 3 are available as plugins for Vue 2, and we could start using those before we upgrade.

@nray, mentioned this as well for Vue 2 with the composition API.

I mentioned the possibility of using the composition API plugin with Vue 2, however the following is mentioned on the plugin's github page :

Note: the primary goal of this package is to allow the community to experiment with the API and provide feedback before it's finalized. The implementation may contain minor inconsistencies with the RFC as the latter gets updated. We do not recommend using this package for production yet at this stage.

😞Since it is also considered "not ready for production" though, I'm not sure if that would offer any advantages over using Vue 3 beta .

In T249725#6105415, @Catrope wrote:

I'll file a task for pre-planning the migration so that we can get ahead of some of those changes, and minimize the amount of work we need to do in the future.

I forgot to mention: I've now filed this task. T251974: Prepare Vue 2 to Vue 3 migration

Thank you, @holger.knust (and thanks for the note, @Catrope)! I'll sign this off next week if someone doesn't beat me to it.