Use appropriate dependencies for browser / node.

[Xiot]

Some of my dependencies have separate entry points depending on whether the are being used on node or in the browser.
It looks like esinstall is originally just using the browser version (see #2214).

What would be awesome for my case, is that if dependencies were loaded depending on the current isSSR flag for the request. If isSSR === true then use the node entry points (module, main), otherwise the user browser entry points (falling back to module, main if browser entry doesn't exist)

[FredKSchott]

Interesting idea!

[Xiot]

I'll start to dig in a little more to see what could be done, but my thought would be something like

1. Option in config if you want to install node dependencies as well.
2. After installing browser dependencies, take another pass and install the node version. Since we know that these are going to be used in node, we could grab the cjs version.
3. When importing via getServerRuntime change the imports to use the node specific one.

Alternatively, since we are just using the packages in node, we could just keep the imports the same and have node pull them from node_modules.

I would have to think about how this would function if packageOptions.source === 'remote' though since (I'm assuming) that SkyPack is mainly set up around serving browser dependencies.

This extends Snowpack past just a frontend build chain, but I think it would be really cool.

[Xiot]

Thinking about this a little further this may only work for simple cases where the backend code doesn't need much setup.
Servers that handle more than just SSR would more than likely have their own http framework complete with their own set of middleware, and wouldn't expose an entry point that takes a basic (req, res) pair.
In my case the framework that I'm using is built on top of Koa which does have a callback method which returns a standard http handler.

The main thing that I'm trying to get out of the setup is HMR in node. But maybe snowpack isn't the best fit for my case.

Currently I have something like nodemon watching for changes and rebuilding my server when files change.

[Xiot]

I dug into this a little more and it appears that esinstall will only ever install the browser dependencies.
This is because in @rollup/plugin-node-resolve uses the passed mainFields to determine whether it should resolve the lookup to to browser field in the package.json here

Because esinstall always passed in the MAIN_FIELDS [here] then @rollup/plugin-node-resolve will always return the resolved path for the browser specific entry point.