Execute Function on DOM or Page Loaded (JavaScript)

on_load.js

// https://stackoverflow.com/questions/11936816/execute-function-after-complete-page-load

document.addEventListener("readystatechange", event => {

    if (event.target.readyState === "interactive") {      //same as:  document.addEventListener("DOMContentLoaded"...   // same as  jQuery.ready
        alert("All HTML DOM elements are accessible");
    }

    if (event.target.readyState === "complete") {
        alert("Now external resources are loaded too, like css,src etc... ");
    }

});

// Or...

document.addEventListener('DOMContentLoaded', function() {
   // your code here
}, false);

window.addEventListener('load', function() {...})