How I’m (Not) Using jQuery – http://youmightnotneedjquery.com/

ajax.js

//https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API
fetch('/data.json')
    .then(res => res.json())
    .then(res => {
      // res is my data
});

event-listeners.js

$("#listOfProducts").on("click", ".productThumb", function() { 
    // STUFF
});

document.addEventListener('click', function(e) {
    if(e.target.className !== 'editLink') return;
    e.preventDefault();

    // STUFF    
}, false);

getting-DOM-items.js

let $field1 = document.querySelector('#field1');
let $field2 = document.querySelector('#field2');

page-load.js

// https://api.jquery.com/ready/
$(document).ready(function() {
    // STUFF HERE
});

// https://developer.mozilla.org/en-US/docs/Web/Events/DOMContentLoaded
document.addEventListener('DOMContentLoaded', function() {
    // STUFF HERE
}, false);