Add invocation of ready function

[Flimm]

The ready JQuery code is:

$(document).ready(function () {});

Currently, the modern equivalent is listed as:

function ready(fn) {
  if (document.readyState !== 'loading') {
    fn();
  } else {
    document.addEventListener('DOMContentLoaded', fn);
  }
}

However, this isn't exactly equivalent, as the ready function does not get called. This pull request makes it equivalent to the JQuery code.