Build: Make babel tranpile smarter by using chrome version (fixes #6367)

[gyandeeps]

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

Test Plan: N/A

Before

    aboutPages.entry.js    2.62 MB       0  [emitted]  aboutPages
           app.entry.js    2.32 MB       1  [emitted]  app

After

    aboutPages.entry.js    2.52 MB       0  [emitted]  aboutPages
           app.entry.js    2.16 MB       1  [emitted]  app

[bbondy]

Thanks!

[bsclifton]

@gyandeeps great find! 😄

[hzoo]

Awesome to see this! Wanted to leave some comments (as a Babel maintainer):

Instead of chrome 54 (since brave is on 56 now), you can do something like

"targets": {
  "browsers": ["last 2 Chrome versions"]
}

Although now that I think about it, we should add one for brave 😝? A package was made for electron babel/babel-preset-env#144

I'd recommend using the useBuiltIns option to reduce the number of polyfills loaded as well. https://github.com/babel/babel-preset-env#usebuiltins if you use babel-polyfill (although not sure if that is loaded or not in the source?

[bbondy]

thanks for the tips @hzoo
@gyandeeps would you mind trying to use useBuiltIns and always use latest for target

[hzoo]

Might need some help with determining where the polyfill is loaded in (if it is at all?)

The way it works currently is that it literally tries to find import "babel-polyfill"; in your code (or require) and then replace that code with the individual imports so it needs to be imported in the entry point file rather than in a script tag or the webpack entry point etc

[gyandeeps]

Thanks @hzoo for feedback.

• I dont think babel-polyfill is used in source code.
• Since we know what version of chrome we use then i guess i can update it to 56.

So just change the chrome version. Any thing i am missing?