刷卡初始化无法获取元素？

Question

我想在初始化时获取元素，但是首先得到的是不确定的

下面是我的代码

html

<div class="swiper-container">
    <div class="swiper-wrapper">
        <div class="swiper-slide">Slide 1</div>
        <div class="swiper-slide">Slide 2</div>
        <div class="swiper-slide">Slide 3</div>
    </div>

    <div class="swiper-button-prev"></div>
    <div class="swiper-button-next"></div>

</div>

javascript

 window.onload = () => {
        new Swiper('.swiper-container', {
            navigation: {
                nextEl: '.swiper-button-next',
                prevEl: '.swiper-button-prev',
            },
            on: {
                init() {
                    console.log('Init complete?')
                    console.log(this.navigation.nextEl) //undefined

                    setTimeout(() => {
                        console.log(this.navigation.nextEl);//object
                    }, 10)
                }
            }
        })
    }