Handle the various of event listener calls.

@param {Event} evt Simple DOM event.
@api private
function change(evt) {
    evt = evt || win.event;

    if ('readystatechange' === evt.type) {
      readystate.change(docReadyState());
      if (complete !== docReadyState()) return;
    }

    if ('load' === evt.type) readystate.change('complete');
    else readystate.change('interactive');

    //
    // House keeping, remove our assigned event listeners.
    //
    (evt.type === 'load' ? win : doc)[off](evt.type, change, false);
  }