Javascript DOMContentLoaded
DOMContentLoaded waits for the entire document to be loaded, but does not
include stylesheets, images, or iframes (you can use the load event if you
care about that).
Generally DOMContentLoaded is most useful when you just need to wait for the
Document Object Model (i.e. th structure of the document itself, rather than its
content) to be ready.
Running a function on DOMContentLoaded
addEventListener('DOMContentLoaded', (event) => {
console.log('DOM Loaded and ready to go.');
});