dynamic loading javascript files with javascript without jQuery (getScript)

getScript.js

function getScript(source, callback) {
  if (Array.isArray(source))
    getScript(source[0], (source.length > 1) ? () => getScript(source.slice(1), callback) : callback);
  else if (!document.querySelector(`script[src="${source}"]`)) {
    var el = document.createElement('script');
    el.onload = callback;
    el.src = source;
    document.head.appendChild(el);
  } else {
    callback();
  }
}

/** Uses **/
getScript([
  "https://cdnjs.cloudflare.com/ajax/libs/anylibrary/1.1.0/main.js",
  "https://cdnjs.cloudflare.com/ajax/libs/anylibrary/1.1.0/main-addon.js",
  "https://cdnjs.cloudflare.com/ajax/libs/anylibrary/1.1.0/main-addon-lang.js"
], () => { alert("all loaded"); });
/*OR*/
getScript("https://cdnjs.cloudflare.com/ajax/libs/anylibrary/1.1.0/main.js", () => { alert("main loaded"); });