Firefox Extension - onPopupClose event?

Question

I have popup in which I need to update the data inside it in reactively. What function or event is needed to track when a popup closes?

Currently my code structure is as follows:

let BG = browser.extension.getBackgroundPage();
let timer = BG.timer;

function updatePageTime(secondsElapsed) {
    const content = document.getElementById("content");
    content.innerHTML = "Current Time Spent: " + timer.getTimeElapsed();
}

document.addEventListener("DOMContentLoaded", function () {
    timer.subscribe(updatePageTime);
});

document.addEventListener("unload", function () {
    timer.unsubscribe(updatePageTime);
});

The problem is that unload and beforeunload do not trigger on popup closes, thus I am unable to stop updates to a non-existant DOM.

Answer 1

Unfortunately I did not see that unload is defined on window and not document. Simply changing the document.addEventListener("unload" to window.addEventListener("unload" fixes the problem.