index.md

---

title: alarms.onAlarm
slug: Mozilla/Add-ons/WebExtensions/API/alarms/onAlarm
page-type: webextension-api-event
tags:
  - API
  - Add-ons
  - Event
  - Extensions
  - Non-standard
  - Reference
  - WebExtensions
  - alarms
  - onAlarm
browser-compat: webextensions.api.alarms.onAlarm

---

{{AddonSidebar()}}

Fired when any alarm set by the extension goes off.

Syntax

browser.alarms.onAlarm.addListener(listener)
browser.alarms.onAlarm.removeListener(listener)
browser.alarms.onAlarm.hasListener(listener)

Events have three functions:

• addListener(listener)

  • : Adds a listener to this event.

• removeListener(listener)

  • : Stop listening to this event. The listener argument is the listener to remove.

• hasListener(listener)

  • : Check whether listener is registered for this event. Returns true if it is listening, false otherwise.

addListener syntax

Parameters

• listener

  • : Function that will be called when this event occurs. The function will be passed the following arguments:

    • alarm

      • : {{WebExtAPIRef('alarms.Alarm')}}. The alarm that fired. Use Alarm.name to figure out which alarm fired.

Examples

Handle an alarm going off:

function handleAlarm(alarmInfo) {
  console.log(`on alarm: ${alarmInfo.name}`);
}

browser.alarms.onAlarm.addListener(handleAlarm);

{{WebExtExamples}}

Browser compatibility

{{Compat}}

Note: This API is based on Chromium's chrome.alarms API.