downloads.onChanged

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

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

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.

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 downloads.DownloadItem object that changed, and the status of all the properties that changed in it.

The downloadDelta object has the following properties available:

id

An integer representing the id of the downloads.DownloadItem that changed.

urlOptional

A downloads.StringDelta object describing a change in a downloads.DownloadItem's url.

filenameOptional

A downloads.StringDelta object describing a change in a downloads.DownloadItem's filename.

dangerOptional

A downloads.StringDelta object describing a change in a downloads.DownloadItem's danger.

mimeOptional

A downloads.StringDelta object describing a change in a downloads.DownloadItem's mime.

startTimeOptional

A downloads.StringDelta object describing a change in a downloads.DownloadItem's startTime.

endTimeOptional

A downloads.StringDelta object describing a change in a downloads.DownloadItem's endTime.

stateOptional

A downloads.StringDelta object describing a change in a downloads.DownloadItem's state.

canResumeOptional

A downloads.BooleanDelta object describing a change in a downloads.DownloadItem's canResume status.

pausedOptional

A downloads.BooleanDelta object describing a change in a downloads.DownloadItem's paused status.

errorOptional

A downloads.StringDelta object describing a change in a downloads.DownloadItem's error status.

totalBytesOptional

A downloads.DoubleDelta object describing a change in a downloads.DownloadItem's totalBytes.

fileSizeOptional

A downloads.DoubleDelta object describing a change in a downloads.DownloadItem's fileSize.

existsOptional

A downloads.BooleanDelta object describing a change in a downloads.DownloadItem's exists status.

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);