Recently I fought - and at the end succeded - to configure two different set of SSH keys for different GitHub account on the same computer.
... more than with Promise, it has to do with core-js Promise polyfill, MutationObserver and IE11. No more spoilers.
This is my checklist for new MacOS installations.
I've started to use Babel when it was still called 6to5, but just recently I learned that it permits to optimize its generated output.