Add :reload Support

[athomasoriginal]

Is your feature request related to a problem? Please describe.

I would like to run nbb from a JS program which is itself running in a "watch loop". The blocker is that dependencies of the nbb scripts won't reload when changes are made to them.

Describe the solution you'd like

I'm not opinionated about the solution, but it sounds like adding support for :reload may resolve this issue.

Describe alternatives you've considered

nbb seeing a file was modified and reloading the namespace accordingly (but this is a naive approach and may not be the responsibility of nbb itself)

Additional context

see eleventy-test-cljs for a "minimal" repro of the problem. Also refer to the original slack thread.

[eval]

Running into this issue as well. Any ideas @borkdude ?

[borkdude]

Sure, :reload support can be added. Do you want me to look into this, or do you want to have any guidance?

[eval]

Pointers would be nice. I guess here's where the magic should happen.... I read dev.md - what are the options to do interactive dev? (using Cider).

[borkdude]

Yes. If the namespace is already loaded, which is discovered here:

nbb/src/nbb/core.cljs

Line 282 in 6485523

(if (sci/eval-form (store/get-ctx) (list 'clojure.core/find-ns (list 'quote libname)))

then we just handle the aliases etc, but don't reload the namespace. I think right there the :reload should be handled.

Note that :reload affects all the namespaces in a require, not just the libspec you write it after.

I don't use CIDER for developing nbb, just bb dev and loading a script on the command line via cli.js and writing tests.

[chr15m]

Not sure if this is of any help but here is a minimal single-script reloader for nbb that seems to work reliably for me. It depends on node-watch.

(ns hello
  (:require
    ["node-watch$default" :as watch]
    [nbb.core :refer [load-file *file*]]))

(print "hello")

(defonce watcher
  (watch *file* (fn [_event-type filename]
                  (js/console.log "Reloading" filename)
                  (load-file filename))))

[borkdude]

Fixed in 1.3.195