feat: webworker ssr target

[patak-dev]

Description

Reworked #3121 as a feat.

#2996 and #3039 reworked the package resolution to ignore the browser field if the plugin is running in ssr mode.

See @frandiox comment, if the target is webworker (ie cloudflare workers) then the browser field should be respected even in ssr mode.

There is a new config option ssr.target:

The default target for the SSR build is a node environment, but you can also run the server in a Web Worker. Packages entry resolution is different for each platform. You can configure the target to be Web Worker using the ssr.target set to 'webworker'.

We already have a build.target but if we reuse it, the users will be forced to modify this option depending on building for the web or using build --ssr. I think it makes sense to be able to define both in the config file.

A targetWeb param to the resolve methods instead of the previous ssr one (I think that targetWeb is better here than targetNode to avoid the need to negate it when using it). In the resolve plugin:

const targetWeb = !ssr || ssrTarget === 'webworker'

#2996 #3039 didn't introduce a regression for Web Workers, because the target was implicitly Node until this point. So they are both fixes for the Node ssr server.

This PR allows ecosystem solutions like vitedge to resolve the browser field as before. There may be other differences that we need to take into account when ssr.target is webworker, but for @frandiox Vite was working without issues before these changes. I think there is the need for extra configuration that may now be included as default when targeting webworkers. For example the resolve.mainFields default. I think these could be added in future PRs. As the SSR feature is still labeled experimental, ssr.target should also be considered experimental.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

[patak-dev]

@frandiox an update on this, we discussed it with Evan and he approves this feature. The ssr.target: 'webworker' will also be handy to define better defaults for things like the ssr.format (we are adding this option in another PR). When it is webworker, the default output format will be es instead of cjs. Once this lands, you could review your setup for vitedge and see if there are some other options defaults that could be pushed upstream.

[frandiox]

@patak-js That's great news! Right now I'm setting the format: 'es' manually but it would be great if Vite takes care of it.

I hope mainFields option will still be available, though, since it needs to be adapted in some scenarios. For example, Vue internals seems to break with ['browser', 'module', 'main'] (Webpack default for webworker target) but work with ['browser', 'main', 'module'].

Thanks for all!