My thoughts are related to a possible feature request. One could possibly use this information to test against previous builds and see if there are any adverse findings. If a first load js delta increases by a certain threshold percentage/amount that a CI pipeline could warn or error to alert the devs something weird may have happened.

I'm not sure if people would use this or find this beneficial.

I'm not sure how this works in the latest app dir

but I can provide some tips that will hopefuly get you on track

the info you're looking for will be inside the .next folder

after a build is compelted

There is code in here that shows how to parse this data for the old pages directory

You could adapt a similiar approach for the app dir

you'll need to poke around the .next folder after a build occurs

and see where this data lives

You can also dig around the source code of next

and figure out how they rendering these stats as part of the build

Another approach

or rather, an indirect approach

is by piping the stdout of next build into a plain text file

and then just parse/regex out the build stats

Throw it at chatgpt and ask it to craft some regex / parser code

for the nextjs build output

Please let me know what you come up with, if you don't I might expand the next-build-size package with this functionality in the future for the app dir specifically

This is nice @linesofcode, it's kind of exactly what I'm talking about, lucky that you're around to see my post.

I think the .next directory doesn't have that data for App Dir. I checked in various ways but didn't see it.

I checked the code last night, and it looks like it builds the output here:
https://github.com/vercel/next.js/blob/93eb32d96a05f5254cc2c3e7b8f47e499517e397/packages/next/src/build/utils.ts#L456C10-L456C22

Although I didn't really dig deep into things.

I was curious if I was missing it in the .next directory but also if there was a way that I wasn't aware of. I don't think there is.

Stdout is one approach but it could be brittle as it relies on Next.js not breaking it.

It seems like you are/were interested in this for Page Router, so that's cool, it isn't just me 😆. I'd like to see if this is an interest for more people. I think it would have to be part of the Next Bundler or like you said capture the output. I'd say pay attention to this thread, I might create a discussion on GitHub. I'll ping here if I do so.

Thanks again @linesofcode

Sounds good!

I'll circle back around to this in the near future and do some research too

this function looks like a good clue

it accepts a build manifest

which i believe is one of the files in the .next output

Yeah I think I'll try figuring out what that buildManifest is tomorrow. It's possible there may already be a way.

@Northern Goshawk hey, I'm curious if you found a solution for this?

Hey @linesofcode sorry for missing this message. I didn't bother investigating further at this time. If this is something you want to run with, feel free to continue. If you do, ping me in any discussion as I'd like to hear other's thoughts 😀.