what's the benefit does this PR bring? Have you ever test it for chromium not download to node_modules with this change?

It fixes the mentioned issue. The extension is now around 4mb instead of 200

I see, I forgot to delete the chromium after I tested the plugin, and published it.

I have two questions:

• With puppeteer set to devDependencies, it's still in the node_modules, we will get the same chromium after my test in the dir puppeteer/puppeteer .
• The extension imports codes from the puppeteer, not only for dev, but running, so chromium is still bundled on publish if I forgot to delete chromium again.

Seems that set to devDependencies doesn't change the circumstances.

Now puppeteer isn't shipped to the user innecessarily, but yes, adding it to devDependencies does mean that it isn't shipped to the user. You don't need to manually delete it in a shell.

Check vsce's documentation: it has a note indicating that devDependencies are automatically ignored, along with all the rest of files in .vscodeignore that are not needed at runtime

Same reasoning in general: everything that you need in order to test or build but not at runtime should go as a dev dependency