browser.tabs.onRemoved.addListener(callback)
browser.tabs.onRemoved.removeListener(listener)
browser.tabs.onRemoved.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 listener is registered for this event. Returns true if it is listening, false otherwise.

callback

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

tabId

integer. ID of the tab that closed.

removeInfo

object. The tab's window ID, and a boolean indicating whether the window is also being closed. See the removeInfo section for more details.

windowId

integer. The window whose tab is closed.

isWindowClosing

boolean. true if the tab is being closed because its window is being closed.

Listen for close events, and log the info:

function handleRemoved(tabId, removeInfo) {
  console.log(`Tab: ${tabId} is closing`);
  console.log(`Window ID: ${removeInfo.windowId}`);
  console.log(`Window is closing: ${removeInfo.isWindowClosing}`);
}

browser.tabs.onRemoved.addListener(handleRemoved);

• tabs-tabs-tabs