Why does an ExperimentalWarning flag get logged as an error?

[john-zaprite]

Since I upgraded my Vercel project to Node v18x, I'm getting a lot of error logs in my console regarding the Fetch API:
Error: (node:15) ExperimentalWarning: The Fetch API is an experimental feature. This feature could change at any time

I understand this is happening since the 17.5 upgrade.

But why don't they get logged as Warnings instead? They are clearly not Errors.

[cjihrig]

I have not used Vercel, but do they treat everything sent to stderr as errors?

[cjihrig]

Yes, that is true.

[john-zaprite]

Right. Really curious about why that is? Seems easy to detect warnings and show them as such. Showing them as Errors seems deliberate so I'm curious about why that might be?

[cjihrig]

Really curious about why that is?

There are a handful of console methods - info(), log(), debug(), warn(), error(), etc. Node.js can only map all of those to stdout and stderr.

Showing them as Errors seems deliberate so I'm curious about why that might be?

This is something that Vercel needs to handle.

[john-zaprite]

Right thanks. So would Vercel have the ability to map a warning from stderr back to a console.warn in their logs? Or can they not tell the difference?

I don't fully understand all this, but seems like I need to get back in touch with Vercel.

Thanks!

[cjihrig]

Based on the contents of vercel/next.js#41124 that you linked to earlier, it seems like they should be able to.

EDIT: Actually, that thread seems to be about warnings that they generate themselves, not Node.js. Either way, there are ways to do it.