tabs.onActivated

Fires when the active tab in a window changes. Note that the tab's URL may not be set at the time this event fired, but you can listen to tabs.onUpdated events to be notified when a URL is set.

browser.tabs.onActivated.addListener(listener)
browser.tabs.onActivated.removeListener(listener)
browser.tabs.onActivated.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:

activeInfo

object. ID of the tab that was made active, and ID of its window.

previousTabId

integer. The ID of the previous activated tab, if that tab is still open.

tabId

integer. The ID of the tab that has become active.

windowId

integer. The ID of the tab's window.

Listen for and log tab activation events:

function handleActivated(activeInfo) {
  console.log("Tab " + activeInfo.tabId +
              " was activated");
}

browser.tabs.onActivated.addListener(handleActivated);

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