Man, good job on writing and puttin you out there, but I made an account just to reply on this. Hate to see things overused just because they're shiny. I noted there was some legacy code that was using loops and wasn't really efficient with the tools we have nowadays. You replaced one completely fine loop with two loops and a ton of allocations. for is not freaking outdated. I think you meant to say "pretty" or "easier to follow", because the "modern" version is way, way less efficient than the original.

Nice explanation of Promises in JavaScript. And the fetching data example is an excellent choice to demonstrate how Promises work.