These are chat archives for opal/opal
ES4-ish? It tries to be compatible with some older IE versions (there's a discussion on how far back to go happening in #1558).
It would be nice to be able to compile to ES6 and then filter that through Babel for code compatible with ES5 and earlier, but that would encode an assumption that either you're okay with ES6 or you've got another filter in your pipeline for ES6 compilation.
Unfortunately, right now, those assumptions can't be made for apps using the Rails asset pipline (according to surveys such as Hampton Catlin's Ruby Survey, that's 85-90% of all Ruby web apps), so telling people to use Webpack would add a lot of friction to the current zero-hassle workflow of
gem 'opal-rails'. :-\