swiper/modules/manipulation/methods/appendSlide.js

export default function appendSlide(slides) {
  const swiper = this;
  const {
    $wrapperEl,
    params
  } = swiper;

  if (params.loop) {
    swiper.loopDestroy();
  }

  if (typeof slides === 'object' && 'length' in slides) {
    for (let i = 0; i < slides.length; i += 1) {
      if (slides[i]) $wrapperEl.append(slides[i]);
    }
  } else {
    $wrapperEl.append(slides);
  }

  if (params.loop) {
    swiper.loopCreate();
  }

  if (!params.observer) {
    swiper.update();
  }
}