Native Vanilla JS $.getScript function with callback.js

function getScript(source, callback) {
  var scriptElement = document.createElement('script');
  var priorScriptElement = document.getElementsByTagName('script')[0];
  scriptElement.async = 1;

  scriptElement.onload = scriptElement.onreadystatechange = function( _, isAbort ) {
    if (isAbort || !scriptElement.readyState || /loaded|complete/.test(scriptElement.readyState) ) {
      scriptElement.onload = scriptElement.onreadystatechange = null;
      scriptElement = undefined;

      if (!isAbort) { 
        if (callback) {
          callback(); 
        }
      }
    }
  };

  scriptElement.src = source;
  priorScriptElement.parentNode.insertBefore(scriptElement, priorScriptElement);
}