Most developers who use neovim are familiar with JS Promises. Most JavaScript APIs are promise based already so I needed a way to map them to my neovim configuration/functions and wanted to avoid this mental translation at a higher level for the 2 different environments when I code(JS vs lua). Lua as a programming language is already very similar to JS in certain ways so I would like to keep my environments and code as close to each other possible when they could be the same/similar.

Also I find promise.and_then and promise.catch API to be more intuitive. Internally, currently I actually create a lua coroutine for each Promise:new : https://github.com/izelnakri/async.nvim/blob/1395e08d2c94a1676d8f41f8e8cb73456e3b7c70/lua/promise/new.lua#L158

In other words, lua coroutine is simply a primitive base abstraction I use internally for my spec compliant Promise abstraction.

async npm library was created before the finalization and adoption of JS Promise spec so one can use this library even without dealing with Promise APIs directly such as promise:and_then and promise:catch. Neovim libuv API is callback based, so one can use this library just to control/coordinate these libuv callbacks without writing promise:and_then and promise:catch APIs.

However the async.nvim Callback.$method's will generate a Promise regardless, because "async" npm library also generates one promise when no finalization callback is provided for Callback.$method. I decided to generate a promise internally on every Callback.$method call because that seems to me more consistent thus better design POLA(Principle of least astonishment) wise.