put babel and browserslist to better use

[8633brown]

maybe more of a proof of concept at the moment but i'm unsure as to whether the builds can be reduced in size any more.

Ive added corejs and setup babel/preset-env to actually be used to polyfill for unsupported browsers. I've used defaults, not ie 11 so you can see how easy it is to modify which browsers are supported or not. currently defaults supports ie 11. So removing the , not ie 11 will compile with support for for ie 11.

I've left the debug flag in so you can see where babel is adding its polyfills. when using , not ie 11 there are far fewer polyfills being added which makes it a little easier to follow whats being added where instead of being cluttered by the ie 11 polyfills.

currently from what i can see the build sizes would go like this:

	build:basic	build:basic-min
original (no preset-env)	950KiB	405 KiB
*chrome 86	946KiB	405KiB
default, no ie 11	1.15MiB	454KiB
defaults	1.38MiB	488KiB
defaults, ie >= 9, safari >= 5.1	1.41Mib	492KiB

* just to prove babel will use no polyfills on a browser which supports everything.

[8633brown]

babel targets property has been changed to defaults, ie >= 9, safari >= 5.1.
I have updated the table to include this in the original comment

[paulrosen]

What's the status of this?

[8633brown]

I'll fix the conflicts when I next look at it again.
It should be pretty much ready to merge especially now the dist folder is included in unpkg

[8633brown]

adds a legacy build which uses babel to keep support for older browsers.

This will be output to the dist/abcjs-legacy-min.js file.
Anyone using older browsers should use this build.
Anyone only needing modern support can use the current dist/abcjs-basic-min.js in any web browser.
Anyone using node + npm to package the project themselves should carry on using import abcjs from 'abcjs'

The modern file still uses babel to transpile the code base to help solve any cross browser discrepancies.

At the moment package.json .main points to index.js. This gives no compatability issues right now however as soon as any ES6 and or TypeScript is used PKG.main should be directed to point at the dist/abc-basic.js file.

[paulrosen]

I think the legacy build needs to be the default for the minified versions. Perhaps the new bundled library should be abcjs-modern-min.js.

For the node version I'm not sure. We have to pick one. Since node_modules are not run through babel, I think it needs to point to the legacy build. And probably have a second entry point for the modern version.

I'm ready to add typescript now.

A big thing that needs to work is the source map - so dev tools works.

[8633brown]

I'm thinking it's maybe overkill providing two versions.

The difference between defaults and defaults, ie >= 9, safari >= 5.1 is only 4KiB.
I think it makes more sense to just use defaults, ie >= 9, safari >= 5.1 and try to improve the project size elsewhere and support only a single instance.
This makes it easier to drop support when you feel happy enough to do so and should keep the typescript build system simpler too as well as keeping the build times down.

[paulrosen]

I agree - the extra build isn't worth it for that. Plus I bet that removing the shims that I put in over the years would be more than 4K.

And it should be easy to add typescript to the build right now - might as well do that so there is only one round of testing.

[8633brown]

I've set up typescript in this now. Everything seems to still be working fine.

So now babel will transpile all .js files and any .ts ts-loader will handle.
The only thing I'm not sure about is how typescript handles core-js transforms.
But I dont think thats is too much of an issue right now as core-js hasn't been used before this PR so I can look into that in the future.

[paulrosen]

I'm revisiting this and doing some testing. It's not good that the package size jumps 80K for the polyfills when I know from browser testing they aren't necessary. And if the user has some other js loaded they might already have the polyfills.

I'm doing some experiments...