Option to write "First Load Size" data to file

Feature request

Is your feature request related to a problem? Please describe.

We’d previously used the bundlesize package in CI in order to monitor the growth of our application and prevent accidental imports of test libs, etc. With the switch to the new chunking strategy, the hash-based names of the new chunks breaks this approach (we previously just watched chunks/commons.*.js). But the new “First Load Size” data could easily replace this functionality, if it were easily accessible (I’m not super keen on redirecting and parsing stdout).

Describe the solution you’d like

Would it be possible to add a configuration option to next.config that enabled also writing the size data to a json file such that it could be then analyzed by other tools?

Describe alternatives you’ve considered

Capturing and parsing the stdout of a yarn build command.

[timneutkens]

I’d like to keep this open, it’s an interesting idea.

[merrywhether]

Stable hashes doesn’t address the issue of trying to reason about the size of a page, since we’d still have to add up the bundle parts included in each page. Something like bundlesize could already work with the regex-addressable page files; the problem is that each page needs an “arbitrary” collection of intermediate JS files. That data is perfectly contained in the pageInfos data structure but not exposed post build so it can’t be used for monitoring.

I know bundle size isn’t everything when it comes to speed of delivery, but it’s a pretty useful first line of defense against someone accidentally including something like faker outside of test files, for instance.