Research a replacement for uglifier's harmony mode for uglifying es6 - terser appears to be the suggested alternative

[jrafanie]

From #9245

FYI, it looks like uglifier's harmony path going forward is in doubt: https://www.github.com/lautis/uglifier/issues/193:

The harmony project in UglifyJS has been without updates for a long time.
Can you warn to use terser when compiling with the harmony option set to true?

They're suggesting we move to terser in the future.

There was a comment here describing how to check all your assets to see which ones are failing to load with uglifier due to this es6 problem. https://www.github.com/lautis/uglifier/issues/127#issuecomment-483313583

[Fryguy]

Another option is to drop uglifier entirely and leave it uncompressed. Or, after that it might possible to use a webpack plugin to do the js compression.

We should also research if Apache has anything for us.

[jrafanie]

mod_deflate might be an option: https://httpd.apache.org/docs/current/mod/mod_deflate.html

[Fryguy]

So there's gzip compression, and then there's uglify-js style compression...we can possibly do both.

I was doing a quick plugin search, and stumbled on https://stackoverflow.com/questions/65298689/uglifyjs-and-webpack-v5, which basically says that the ugjlify-js webpack plugin only works with webpack 4, but on webpack 5 there's a terser plugin instead. I'm wondering if we can just use it directly in our webpack config and then we don't need any Rails-side js compression.

https://github.com/webpack-contrib/terser-webpack-plugin