Services

System state as signals, from halo/services. A service runs only while something reads it; reading battery.percent() in a widget is all it takes.

A status strip

import {
  audio,
  battery,
  drag,
  frontApp,
  network,
  power,
  session,
  system,
} from "halo/services";

<Text>
  {() => `${battery.percent()}% · ${Math.round((system.cpu() ?? 0) * 100)}% CPU`}
</Text>;

Service	Values	Updates
`battery`	`present`, `percent`, `charging`, `source` (`ac`/`battery`), `minutesRemaining`	on power changes
`audio`	`volume` (0–1), `muted`, `device`	on volume or device change
`network`	`connected`, `type` (`wifi`, `ethernet`, …, `none`), `expensive`, `constrained`	on network change
`frontApp`	`name`, `bundleId`, `pid`	on app switch
`power`	`lowPowerMode`, `thermal` (`nominal`, `fair`, `serious`, `critical`)	on change
`session`	`locked`, `displaysAsleep`, `lastWake` (ms; changes on every wake)	on change
`drag`	`active` (files are being dragged anywhere; true until the drop lands), `outgoing` (started in halo)	while the button is held
`system`	`cpu(ms?)`, `memory(ms?)`, `memoryUsed`, `memoryTotal`	every `ms` (default 2000)
`clock`	`format(pattern)`	every minute or second

Values are undefined until the first reading arrives.

Actions

audio.setVolume(0.4);
audio.toggleMuted();
<Box onScroll={({ dy }) => audio.setVolume((audio.volume() ?? 0) + dy * 0.01)} />;

audio.volume() is undefined for outputs with no software volume (many HDMI and DisplayPort monitors); setting it returns false there.

Notes

frontApp.bundleId() works with <Image app={…}> for the app's icon.
No Wi-Fi network name: it needs a Location permission halo can't ask for. No Focus/Do Not Disturb either: macOS protects its state and the public API needs an authorization prompt.
session.locked() relies on undocumented macOS signals, so it may stay undefined on future versions.
Use session.lastWake() in an effect to refresh data after sleep.
system has no notification to follow, so it samples; pick the slowest interval you can live with.

Reference: halo/services. Full example: examples/services.