index.md

---

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

---

{{AddonSidebar()}}

The onChanged() event of the {{WebExtAPIRef("downloads")}} API is fired when any of a {{WebExtAPIRef('downloads.DownloadItem')}}'s properties changes (except for bytesReceived).

The listener is passed a downloadDelta as a parameter — an object containing the downloadId of the {{WebExtAPIRef('downloads.DownloadItem')}} object in question, plus the status of all the properties that changed.

Syntax

browser.downloads.onChanged.addListener(listener)
browser.downloads.onChanged.removeListener(listener)
browser.downloads.onChanged.hasListener(listener)

Events have three functions:

• addListener(callback)

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

addListener syntax

Parameters

• callback

  • : A callback function that will be called when this event occurs. This function will be passed the following arguments:

    • downloadDelta

      • : An object representing the {{WebExtAPIRef('downloads.DownloadItem')}} object that changed, and the status of all the properties that changed in it. See the downloadDelta section for more details.

Additional objects

downloadDelta

The downloadDelta object has the following properties available:

• id

  • : An integer representing the id of the {{WebExtAPIRef('downloads.DownloadItem')}} that changed.

• url {{optional_inline}}

  • : A {{WebExtAPIRef('downloads.StringDelta')}} object describing a change in a {{WebExtAPIRef('downloads.DownloadItem')}}'s url.

• filename {{optional_inline}}

  • : A {{WebExtAPIRef('downloads.StringDelta')}} object describing a change in a {{WebExtAPIRef('downloads.DownloadItem')}}'s filename.

• danger {{optional_inline}}

  • : A {{WebExtAPIRef('downloads.StringDelta')}} object describing a change in a {{WebExtAPIRef('downloads.DownloadItem')}}'s danger.

• mime {{optional_inline}}

  • : A {{WebExtAPIRef('downloads.StringDelta')}} object describing a change in a {{WebExtAPIRef('downloads.DownloadItem')}}'s mime.

• startTime {{optional_inline}}

  • : A {{WebExtAPIRef('downloads.StringDelta')}} object describing a change in a {{WebExtAPIRef('downloads.DownloadItem')}}'s startTime.

• endTime {{optional_inline}}

  • : A {{WebExtAPIRef('downloads.StringDelta')}} object describing a change in a {{WebExtAPIRef('downloads.DownloadItem')}}'s endTime.

• state {{optional_inline}}

  • : A {{WebExtAPIRef('downloads.StringDelta')}} object describing a change in a {{WebExtAPIRef('downloads.DownloadItem')}}'s state.

• canResume {{optional_inline}}

  • : A {{WebExtAPIRef('downloads.BooleanDelta')}} object describing a change in a {{WebExtAPIRef('downloads.DownloadItem')}}'s canResume status.

• paused {{optional_inline}}

  • : A {{WebExtAPIRef('downloads.BooleanDelta')}} object describing a change in a {{WebExtAPIRef('downloads.DownloadItem')}}'s paused status.

• error {{optional_inline}}

  • : A {{WebExtAPIRef('downloads.StringDelta')}} object describing a change in a {{WebExtAPIRef('downloads.DownloadItem')}}'s error status.

• totalBytes {{optional_inline}}

  • : A {{WebExtAPIRef('downloads.DoubleDelta')}} object describing a change in a {{WebExtAPIRef('downloads.DownloadItem')}}'s totalBytes.

• fileSize {{optional_inline}}

  • : A {{WebExtAPIRef('downloads.DoubleDelta')}} object describing a change in a {{WebExtAPIRef('downloads.DownloadItem')}}'s fileSize.

• exists {{optional_inline}}

  • : A {{WebExtAPIRef('downloads.BooleanDelta')}} object describing a change in a {{WebExtAPIRef('downloads.DownloadItem')}}'s exists status.

Browser compatibility

{{Compat}}

Examples

Log a message when downloads complete:

function handleChanged(delta) {
  if (delta.state && delta.state.current === "complete") {
    console.log(`Download ${delta.id} has completed.`);
  }
}

browser.downloads.onChanged.addListener(handleChanged);

{{WebExtExamples}}

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