A way to call a JavaScript function on DOMContentLoaded or after, no rush. Great for non-essential async code.

onwheneva.js

var test = () => {
  console.log('fired on DOMContentLoaded or after');
}

window.onwheneva = test;

document.readyState !== 'loading' ? onwheneva() :
 document.addEventListener('DOMContentLoaded', onwheneva);