BookStack/resources/assets/js/components/back-to-top.js

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JavaScript
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class BackToTop {
constructor(elem) {
this.elem = elem;
this.targetElem = document.getElementById('header');
this.showing = false;
this.breakPoint = 1200;
if (document.body.classList.contains('flexbox')) {
this.elem.style.display = 'none';
return;
}
this.elem.addEventListener('click', this.scrollToTop.bind(this));
window.addEventListener('scroll', this.onPageScroll.bind(this));
}
onPageScroll() {
let scrollTopPos = document.documentElement.scrollTop || document.body.scrollTop || 0;
if (!this.showing && scrollTopPos > this.breakPoint) {
this.elem.style.display = 'block';
this.showing = true;
setTimeout(() => {
this.elem.style.opacity = 0.4;
}, 1);
} else if (this.showing && scrollTopPos < this.breakPoint) {
this.elem.style.opacity = 0;
this.showing = false;
setTimeout(() => {
this.elem.style.display = 'none';
}, 500);
}
}
scrollToTop() {
let targetTop = this.targetElem.getBoundingClientRect().top;
let scrollElem = document.documentElement.scrollTop ? document.documentElement : document.body;
let duration = 300;
let start = Date.now();
let scrollStart = this.targetElem.getBoundingClientRect().top;
function setPos() {
let percentComplete = (1-((Date.now() - start) / duration));
let target = Math.abs(percentComplete * scrollStart);
if (percentComplete > 0) {
scrollElem.scrollTop = target;
requestAnimationFrame(setPos.bind(this));
} else {
scrollElem.scrollTop = targetTop;
}
}
requestAnimationFrame(setPos.bind(this));
}
}
export default BackToTop;