An implementation of Promise
similar to Promise/A+.
I've found that being able to yield anywhere causes lots of bugs. In Rodux, I explicitly made it impossible to yield in a change handler because of the sheer number of bugs that occured when callbacks randomly yielded.
As such, I think that Roblox needs an object-based async primitive. It's not important to me whether these are Promises, Observables, Task objects, or Futures.
The important traits are:
This Promise implementation attempts to satisfy those traits.
Promise.new((resolve, reject) -> nil) -> Promise
Promise.resolve(value) -> Promise
Promise.reject(value) -> Promise
Promise.is(object) -> bool
Promise.all(array) -> array
Promise:andThen(successHandler, [failureHandler]) -> Promise
then
method.Promise:catch(failureHandler) -> Promise
Promise:andThen(nil, failureHandler)
.Promise:await() -> ok, value
ok
as a bool, followed by the value that the promise returned.This Promise implementation finished synchronously. In order to wrap an existing async API, you should use spawn
or delay
in order to prevent your calling thread from accidentally yielding.
local HttpService = game:GetService("HttpService")
-- A light wrapper around HttpService
-- Ideally, you do this once per project per async method that you use.
local function httpGet(url)
return Promise.new(function(resolve, reject)
-- Spawn to prevent yielding, since GetAsync yields.
spawn(function()
local ok, result = pcall(HttpService.GetAsync, HttpService, url)
if ok then
resolve(result)
else
reject(result)
end
end)
end)
end
-- Usage
httpGet("https://google.com")
:andThen(function(body)
print("Here's the Google homepage:", body)
end)
:catch(function(err)
warn("We failed to get the Google homepage!", err)
end)
Promise.wrapAsync
This project is available under the CC0 license. See LICENSE for details.