Bump to babel 7 and switch from es2015 to babel-preset-env

[adrienharnay]

Hello,

I figured that it would be great for this project to have a browserlists file and to use @babel/preset-env to ensure support for older browsers is never compromised.

Would you be interested in me submitting a pull request?

Cheers

[kossnocorp]

That's a good question. We intentionally didn't introduce modern JS features because you never know what Babel would generate or which polyfills it would include and how this will affect the build size. That's a pandora box that I would rather not open. But I understand the concern. Can it be solved using ESLint?

[adrienharnay]

I don't think this so...

What do you think of this strategy:

• upgrade to Babel 7
• implement @babel/preset-env with a browserslist file
• compare old build size to new build size
• implement https://github.com/siddharthkp/bundlesize to ensure the size of the build never increases passed a certain ceiling (to be defined)

I've implemented this on a few projects so I could do a PR if you think this could work for date-fns 🙂

PS: it would allow maintainers to use new JS features, which are sometimes more readable/performant that their old alternatives

[kossnocorp]

That will add a lot of additional overhead to the maintenance process. I'm not concerned with the overall bundle size but rather with the size of individual functions. A new locale will always add a lot of code, and it's okay while even 0.1Kb increase in a single function could be a problem.

Quick googling showed that the problem could be solved with eslint-plugin-compat that reads the browserslist file, so I'm ok with upgrading Babel and adding browserlist but not @babel/preset-env. Also, we already use size-limit for checking bundle size but do it manually when necessary.

[adrienharnay]

Ah gotcha! Do you want me to file the PR for Babel 7 and eslint-plugin-compat?

[kossnocorp]

That would be helpful, thanks! 🙏

[nanomosfet]

@adrienharnay Do you have any examples of comparing build sizes? I am pretty interested in seeing how its done.

[adrienharnay]

Hey, sorry for the delay, the past weeks have been busy. Well I'm using https://github.com/siddharthkp/bundlesize along with its Github build status integration, I have a config in my package.json to specify the thresholds and it compares the size of the build on my PRs to the size on master. I don't have any concrete example to show as the repositories are private, but it's fairly easy to set up using the docs (took me 10min). Tell me if I can provide more info on this :)