Migration guide

[Rich-Harris]

v2 to v3 needs a blog post describing the changes, with examples.

Will also need to get svelte-upgrade finished

[himynameisdave]

Yeah I would love to help out here if I can, but I'm pretty unclear about all the changes and what a proper migration would look like. Sadly the CHANGELOG isn't much help.

If someone can provide me some key points I could write out some examples to help here.

[red8012]

It has been 2 months since 3.0.0 released. People just love it. I think it is now fairly stable for most users. @Rich-Harris do you recommend people with existing v2 projects start migrating to v3? If so, is there any ETA for the migration guide (as well as svelte-upgrade)?

Thanks in advance.

[praneybehl]

Hi all, I have a few svelte apps that I'm looking to update. Is there a migration guide?

[tivac]

No guide or updates to the tooling that I'm aware of, we're currently using https://github.com/tivac/svelte-translator in production and I think it's been pretty successful. Biggest limitation is a lack of support for slotted content but given the v2 component APIs lack of hooks around that I don't think it's possible to fix atm.

[aaronjensen]

The original blog post written in April 2019 says "In the coming days we'll release a migration guide and an updated version of which will do the best it can to automate the process...", yet the v3 branch on svelte-upgrade hasn't seen any changes in almost a year.

We have a svelte 2 project that we just inherited--is it worth waiting longer or should we begin the port to React?

[Conduitry]

We're spread pretty thin, and I wouldn't hold my breath on the v2->v3 migration tool getting finished any time soon - but I'm not sure why, absent a migration tool, your only alternative is to manually port to React. If that's a threat, it's not a very effective one.

[TehShrike]

@aaronjensen firing up the v3 branch and running it against your project would be a lot less work than migrating.

[aaronjensen]

Hi @Conduitry, sorry—I wrote that in a bit of a hurry and with some fear and I realize it looked like a threat. I'm sorry about that, that wasn't my intention at all. It's not that it's our only alternative, it's just where most of our skills are. Personally, I'm excited about svelte and have been for a long time but I haven't had a chance to use it. This would be a great chance for that, but I was worried about the idea of being stuck on v2 since there didn't seem to be an upgrade guide and the changes seemed big, but that's likely just my naïveté.

Good to know that the v3 branch should work to help us migrate, I'll definitely try that out. I was just concerned about migrating from something we don't have familiarity with to something we don't have familiarity with. The app itself isn't massive, so a port to React is likely a real (but unfortunate) possibility.

In any case, thank you for the update and the suggestion. We'll try it out. If there are issues, would it be worth opening issues on the upgrader repo or would we be better off fixing them manually? Thanks!

[tivac]

@aaronjensen I probably wouldn't bother, I doubt the upgrade tooling is getting any more work put into it. My svelte-translator project can help you slowly transition a codebase to svelte 3 if you don't need some advanced features, but for a small app you're probably better off manually porting.

I've found I can port a component pretty quickly after some practice, and generally get it right oh the first try. Svelte v3 is awesome in its clarity.