Fix minimization of bundles

[appden]

The default minimizer created by Webpack does not provide a test options, so the default tests just for .js files. Since we rely on a different extension for our output bundles, we need to explicitly use UglifyJsPlugin ourselves.

Fixes #458

[thymikee]

Looks ok. @zamotany @satya164?

[satya164]

Seems the plugin uses uglify-es which is unmaintained and causes bugs with React https://twitter.com/greweb/status/1013093979309727752?s=19

Is there a way to use V2? Maybe it'll be better to switch to babili?

[hedgepigdaniel]

terser is a drop in replacement for uglify (its a fork which is maintained). From what I understand, its faster than babili. Turning off compression makes the process about 3x faster again, with minimal/no increase in filesize.

[appden]

Not sure which direction you guys would like to go here. Unfortunately, babel-minify-webpack-plugin doesn't look well maintained at this point either.

Terser looks great. We would either recommend users swap it in with the Yarn resolutions hack, or instead depend on this terser-webpack-plugin instead (my personal recommendation).

It looks like this will be temporary dependency since Webpack 5 will include its own MinimizerWebpackPlugin (according to this comment), which will support Terser.

[drgx]

Hi @appden ,Thanks for you PR but i want to share my finding that related to haul minification:

• Latest haul version my bundle size was 7MB (minification not working)
• With you minify changes the bundle size reduce to 4MB
• Downgrade to haul 1.0.0-beta.13 (before webpack 4) the size reduce to 2.7MB
• Using metro bundle the bundle size 2.5MB
  After your magnification changes, the bundle size still bigger than pervious haul version and metro. 😢
  Our android team really strict on the RN bundle size. Hopefully we can find a way to reduce the bundle size so it same or smaller than metro version 🙇

Great work btw! 👍