Using buttons to control PageFly slider

.js

window.addEventListener('load', () => {
    const id = Object.getOwnPropertyNames(__pagefly_slideshows__);
    const slideId = id[0];
    const slideObj = __pagefly_slideshows__[slideId];
    const firstSlide = document.getElementById('button-1')
    const secondSlide = document.getElementById('button-2')
    const lastSlide = document.getElementById('button-3')
    firstSlide.addEventListener("click", function () {
        slideObj.scrollItem(0);
    })
    secondSlide.addEventListener("click", function () {
        slideObj.scrollItem(1);
    })
    lastSlide.addEventListener("click", function () {
        slideObj.scrollItem(2);
    })
})

The script used to use buttons to control PageFly slider