Background Script Chrome Extension

Hello, I am looking for a way to get a badge to show up after a timed amount when the chrome extension is closed. How can I run "myFunction" in the background.js? The code below is from popup.js

document.addEventListener('DOMContentLoaded', function(){
    hide("second")
    document.querySelector('#start').addEventListener('click', myFunction);
    document.querySelector('#start').addEventListener('click', close);
    chrome.browserAction.setBadgeText({"text": "Break Time"});
});
function myFunction(){
    setTimeout(function(){
        chrome.browserAction.setBadgeText({"text": "5 sec"});
    }, 5000); 
}
function show(section)
{
    document.getElementById(section).style.display = "block";
}
function hide(section)
{
    document.getElementById(section).style.display = "none";}

function close() {
    hide("time-selection");
    window.close();
    editing = false;  
}