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is this still true, even for script type=module? 🤯 cc: @chromium.social … can’t for the life of me find the message but thank you to the person at @perfnow.bsky.social who sent this my way ❤️ web.dev/learn/perfor...

I don't think it matters for the web. But does for Node and the like: v8.dev/features/mod...

okay, so the docs I linked are outdated?

And yet oddly written after the doc I linked! @kevinfarrugia.bsky.social did you write web.dev/learn/perfor... ? Got any more info on mjs file extension?

I _think_ @kevinfarrugia.bsky.social thought the impact was minimal (but if it's even slight I think we should reconsider our default format in @nuxt.com and possibly also in @vite.dev). the key thing I'd like to confirm is that it really is the case first ...

for example, this commit (if it's the _only_ optimisation) seems to suggest it might just apply to link preloads where `modulepreload` is not explicitly set: github.com/chromium/chr...

Yea, that fix is about treating <link rel=preload href=foo.mjs> as if it's a modulepreload. I don't think Chromium has any mjs-specific things that cannot be achieved in better ways.

so this isn't correct? > Where V8 is concerned, you effectively opt out of streaming compilation when you ship JavaScript modules in production using the .js extension.

"The core problem is that when starting streaming, we need to guess whether the script will be used as a module or not, since that will affect how the script is parsed. If we get that guess wrong, we just silently ignore the streaming parsing results and parse it again."

I tested many different scenarios manually and couldn't observe any difference. I had suggested that they include a trace event to be able to recognize when the streamed script is dropped but I don't think it was done.

The bug ticket requesting the change in the module: issuetracker.google.com/issues/31000... Relevant bit: > Streaming compilation footguns: > Use .mjs extension instead of .js extension when shipping ES6 module code in prod—this breaks streaming compilation!

When testing this locally, the trace event `BackgroundCompileTask::Run` (source.chromium.org/chromium/chr...) was visible for both file extensions, however they later clarified that it will begin streaming compilation in both cases but drop it in the case of `.js`.

thank you for digging this out. is it possible that maybe background compilation is not supported for modules _at all_ regardless of extension? source.chromium.org/chromium/chr...

V8 team advised that I create a crbug to add a trace event when the streaming parsing results are dropped: issues.chromium.org/u/1/issues/3...