Run js during app installation process from app loader?

[thyttan]

Hi!

Is there a way to have some js run during the installation process when loading apps to the Bangle?

For the twenties app we now have a boot file that sets up the app and then deletes itself: https://github.com/espruino/BangleApps/blob/7537413ba30c761de46befd54e46b96da7c54aa7/apps/twenties/boot.js

This works OK, but it has the side effect of having to regenerate the .boot0 file again when twenties.boot.js was deleted. Not a big deal, but a bit jarring.

I also now want to do something similar with the quicklaunch app for updating its settings in quicklaunch.json. So it would be nice to have something a bit more streamlined.

Could that setting up be done during the installation process instead to avoid the boot file "hack"?

I tried to understand if the "evaluate": true in metadata could achieve this but I don't think so?

Thanks!

[cookesan]

Yes, but evaluate: true is not the part I would use for this.

evaluate only changes how uploaded file content is handled: the data is not quoted as a string before upload, so it is useful for entries like generated image/content expressions. It is not really a post-install hook.

For install-time code, the App Loader already has the RAM path. In metadata.json storage entries, name: "RAM" means the code is sent directly to the Bangle and is not saved as a file. Existing apps use the same pattern from custom pages, for example sending:

{ name: "RAM", content: js }

For the Twenties case, the shape I would try is to upload the library first and then add a RAM entry that performs the setup:

"storage": [
  { "name": "twenties", "url": "lib.js" },
  { "name": "RAM", "content": "require('twenties').setup();" }
]

That makes the setup run during upload instead of keeping a temporary twenties.boot.js around until the next boot.

If the setup needs App Loader UI choices or connected-device information, use a custom page with customConnect: true, then call sendCustomizedApp with the normal storage entries plus a final { name: "RAM", content: "..." } entry. I would keep app type: "RAM" for tools that do not install a normal app at all, like the existing assisted GPS and firmware update tools.

[thyttan]

Thank you - that makes sense and works for the twenties app!

Just as a follow up, do you have a suggestion for running custom uninstall scripts when deleting an app from the Bangle using the app loader? It would be cool to delete the alarm set by twenties when uninstalling. Not very important though, since it will stop rearming itself anyway.

[cookesan]

I do not see a current App Loader hook for running arbitrary code on uninstall.

The cleanup path the loader already has is file-based: metadata.json has data for files the app may write, and the generated app.info uses that so those files can be removed when the app is deleted. That is good for app-owned settings/data files, but it does not help with one entry inside a shared file.

For Twenties specifically, I would not add sched.json to data, because that file belongs to the scheduler and contains all alarms/timers. Deleting it would be too broad.

The good part is that the current scheduled JS already starts with:

require("sched").setAlarm("twenties", undefined);

so if the app is removed before the next buzz, that hidden alarm should delete itself before it tries to re-run the Twenties setup. It is not as tidy as uninstall-time cleanup, but it is a reasonable fallback.

If you want this to be clean at delete time, I think it would need a small App Loader feature rather than metadata today. Something like a documented uninstall command/hook, or a scheduler-aware convention that removes alarms with appid: "twenties", would avoid having every app invent its own cleanup path while also avoiding deletion of shared scheduler state.

[thyttan]

Thank you again - informative and seems like a very complete answer :)

Out of curiosity, do you program for and use a Bangle.js watch yourself? Or have you managed to have an AI keep tabs on all necessary parts to answer like this (I see "smithersai/smithers" pinned on your profile)? Impressive either way!

[cookesan]

I use tool-assisted surfacing and then go on in and answer interesting threads, but only where I can be helpful!

[thyttan]

That's kind! thanks again :)