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nbb 2026-04-09
Gregory Bleiker 2026-04-09T16:58:16.140939Z
I'm trying to figure out promises on the repl: The example below once calls load-file and once I paste the code. They behave differently. I probably have to tell the pasted version to await, but I can't figure out how.
user=> (ns user
#_=> (:require [promesa.core :as p]))
#_=>
#_=> (def kv-promise (js/Deno.openKv "something"))
#_=>
#_=> (-> kv-promise
#_=> (p/then (fn [kv]
#_=> (prn "Got KV instance")
#_=> (let [result (.set kv #js["test"] #js{:a "b"})]
#_=> (prn "Set returned:" (type result))
#_=> result)))
#_=> (p/then (fn [set-result]
#_=> (prn "Set completed with result:" set-result)
#_=> (println "done")
#_=> set-result))
#_=> (p/then (fn [_] (println "did we get here?")))
#_=> (p/catch (fn [err]
#_=> (prn "Error occurred:" err)
#_=> (prn "Error stack:" (.-stack err)))))
#object[Lt user]
#'user/kv-promise
#<Promise[pending:23]user=> (nbb.core/load-file "kvtest.clj")
"Got KV instance"
"Set returned:" #object[Promise]
"Set completed with result:" #js {:ok true, :versionstamp "00000000000000190000"}
done
did we get here?
nilGregory Bleiker 2026-04-13T17:09:40.053839Z
@borkdude works, awesome! Sorry for the testing delay.
Gregory Bleiker 2026-04-13T17:10:47.861429Z
I find working with promises the hardest part at the moment.. is there anything in clj-kondo that helps, like spotting un-awaited promises?
borkdude 2026-04-13T17:52:25.726899Z
Actually you can now use async/await in SCI and thus in nbb, which makes writing async code easier
Gregory Bleiker 2026-04-13T19:09:20.903539Z
Will this work with any kind of promises, like the one from deno above?
borkdude 2026-04-13T19:10:40.957779Z
good question. I expect Deno doesn't have a custom Promise, just a js/Promise, but SCI might not have accounted for mixing with the custom promesa promesas (thenable). I'll test
borkdude 2026-04-13T19:11:46.971649Z
seems to work:
user=> (def p (p/resolved 1))
#'user/p
user=> (defn ^:async my-fn [] (let [x (await p)] (inc x)))
#'user/my-fn
user=> (my-fn)
#<Promise 2>borkdude 2026-04-09T18:51:30.941469Z
I think the problem is that nbb isn't aware of promesa's custom promise type. Can you try to convert it to a platform promise and then see if the behavior is still different?
borkdude 2026-04-09T18:52:02.656019Z
nbb has a couple of (instance? js/Promise x) checks and it should try to check for .then instead
borkdude 2026-04-09T18:53:50.830999Z
Just wrap it in (js/Promise.resolve ...)
borkdude 2026-04-09T18:54:11.059249Z
if that fixes the issue, please make an nbb github issue and I'll make a new release with the fix
Gregory Bleiker 2026-04-09T20:15:17.537139Z
@borkdude could you check if the jsr publish is broken? The version there is still 1.3.205
borkdude 2026-04-09T20:31:03.490019Z
try again