code: function ready(callback) {
    let onLoaded = (event) => {
      if (document.addEventListener) {
        document.removeEventListener('DOMContentLoaded', onLoaded, false);
        window.removeEventListener('load', onLoaded, false);
      }
      else if (document.attachEvent) {
        document.detachEvent('onreadystatechange', onLoaded);
        window.detachEvent('onload', onLoaded);
      }
  
      setTimeout(callback, 1);
    };
  
    if (document.readyState === 'complete') return setTimeout(callback, 1);
  
    if (document.addEventListener) {
      document.addEventListener('DOMContentLoaded', onLoaded, false);
      window.addEventListener('load', onLoaded, false);
    }
    else if (document.attachEvent) {
      document.attachEvent('onreadystatechange', onLoaded);
      window.attachEvent('onload', onLoaded);
    }
  }
docs: Helper function for invoking a callback when the DOM is ready.
  
  @param {Function} callback
  
  @private