Script

The JavaScript runtime, the quasar API, and its limits.

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The script block holds a station’s logic, in JavaScript. Every function the interface or hooks call must be exported:

export function player_count() {
  const out = quasar.exec('minecraft', ['rcon-cli', 'list']).stdout
  return { data: { value: out.match(/There are (\d+)/)[1] } }
}

An action receives one argument: the form values, the row’s fields, or {q} for a search.

The runtime

Scripts are synchronous: no async, no promises, no setTimeout. A function runs and returns.
There is no fetch, require, import, file system or network. The only way to reach anything is the quasar object.
Each call runs in a new process, which stops afterwards. Nothing is kept between calls, except what you save in the store.
Calling something a permission doesn’t cover throws an error that names the missing permission.

API

Application

quasar.app                 // {id, name, domain, status, params, image}
quasar.app.params.VERSION  // answers given when deploying

With the lifecycle permission, for the listed verbs:

quasar.app.start()
quasar.app.stop()
quasar.app.restart()
quasar.app.redeploy()
quasar.app.setImage('nginx:1.27')

Environment

Needs env, for the declared keys.

quasar.env.get('MINECRAFT_VERSION')
quasar.env.set('MINECRAFT_VERSION', '1.21.4')   // applied at the next deployment

Containers

quasar.exec('web', ['sh', '-c', 'nginx -v'])    // -> {code, stdout, stderr}   needs exec
quasar.logs('web', {tail: 100, since: '1h'})    // -> string                  needs logs

Files

Needs files. Paths are relative to the application’s folder.

quasar.files.list('data/mods')              // -> [{name, size, dir, mtime}]
quasar.files.read('data/server.properties') // -> string
quasar.files.readBytes('data/world.zip')    // -> Uint8Array
quasar.files.write('data/notes.txt', text)  // string or Uint8Array, atomic
quasar.files.delete('data/old.jar')
quasar.files.mkdir('data/backups')

HTTP

const r = quasar.http.get(url, opts)   // also quasar.http.post(url, opts)
r.status    // number
r.headers
r.body      // text
r.json()    // parsed JSON
r.bytes()   // Uint8Array

quasar.service('web', 80)              // base URL of a service on the internal network

External hosts need net.external; the app’s own services need net.internal.

Binary files

Use bytes(), not body, for anything that isn’t text (archives, images, .jar files). body is decoded as UTF-8 and silently corrupts binary data.

quasar.files.write('data/mods/mod.jar', quasar.http.get(url).bytes())

Store

A small key-value space for this station and this application. No permission needed.

quasar.store.get('count')
quasar.store.set('count', 3)     // any JSON value
quasar.store.delete('count')
quasar.store.keys()

Limited to 256 KB per application. For values over time, use series.

Series

Measurements over time, drawn by a chart panel. No permission needed. See series.

quasar.series.record('players', 12)
quasar.series.read('players', {hours: 24})   // -> [{at, value}], oldest first
quasar.series.names()

Other

quasar.notify('Backup finished')          // needs notify
quasar.log('step', 3, 'done')             // the station's own log, visible in the interface
quasar.progress(40, 'Downloading mods')   // long actions only

Limits

Limits are enforced from outside the script’s process. A station that hits one fails its panel; the dashboard and other applications are not affected.

Limit	Panel source	Action	Hook
Run time	10 s	60 s	120 s
Returned value	1 MB	1 MB	—

Limit	Value
Memory	128 MB
`quasar.exec` output	1 MB per call
`quasar.http` response	8 MB per call
`quasar.files.read`	4 MB
`quasar.store`	256 KB per application
Series	8 per application

For work longer than 60 seconds, use a long action.