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const SCROLL_DELTA_X = 48;
const SCROLL_DELTA_Y = 48;
const SMOOTH_SCROLL_DURATION = 150;
const isVisible = (element) => {
let rect = element.getBoundingClientRect();
if (rect.width === 0 || rect.height === 0) {
return false;
}
if (rect.right < 0 && rect.bottom < 0) {
return false;
}
if (window.innerWidth < rect.left && window.innerHeight < rect.top) {
return false;
}
let { display, visibility } = window.getComputedStyle(element);
if (display === 'none' || visibility === 'hidden') {
return false;
}
return true;
};
const isScrollableStyle = (element) => {
let { overflowX, overflowY } = window.getComputedStyle(element);
return !(overflowX !== 'scroll' && overflowX !== 'auto' &&
overflowY !== 'scroll' && overflowY !== 'auto');
};
const isOverflowed = (element) => {
return element.scrollWidth > element.clientWidth ||
element.scrollHeight > element.clientHeight;
};
// Find a visiable and scrollable element by depth-first search. Currently
// this method is called by each scrolling, and the returned value of this
// method is not cached. That does not cause performance issue because in the
// most pages, the window is root element i,e, documentElement.
const findScrollable = (element) => {
if (isScrollableStyle(element) && isOverflowed(element)) {
return element;
}
let children = Array.prototype
.filter.call(element.children, e => isVisible(e));
for (let child of children) {
let scrollable = findScrollable(child);
if (scrollable) {
return scrollable;
}
}
return null;
};
const scrollTarget = () => {
if (isOverflowed(window.document.documentElement)) {
return window.document.documentElement;
}
if (isOverflowed(window.document.body)) {
return window.document.body;
}
let target = findScrollable(window.document.documentElement);
if (target) {
return target;
}
return window.document.documentElement;
};
const easing = (t) => {
if (t < 1) {
return t * t;
}
return -(t - 1) * (t - 1) + 1;
};
const smoothScroll = (element, x, y) => {
let startX = element.scrollTop;
let startY = element.scrollTop;
let distanceX = x - startX;
let distanceY = y - startY;
let timeStart = 0;
const loop = (timeCurrent) => {
if (!timeStart) {
timeStart = timeCurrent;
}
let timeElapsed = timeCurrent - timeStart;
let t = timeElapsed / SMOOTH_SCROLL_DURATION;
let nextX = startX + distanceX * easing(t);
let nextY = startY + distanceY * easing(t);
window.scrollTo(nextX, nextY);
if (timeElapsed < SMOOTH_SCROLL_DURATION) {
window.requestAnimationFrame(loop);
} else {
element.scrollTo(x, y);
}
};
window.requestAnimationFrame(loop);
};
const roughScroll = (element, x, y) => {
element.scrollTo(x, y);
};
const scroll = (element, x, y, smooth) => {
if (smooth) {
smoothScroll(element, x, y);
} else {
roughScroll(element, x, y);
}
};
const scrollVertically = (count, smooth) => {
let target = scrollTarget();
let x = target.scrollLeft;
let y = target.scrollTop + SCROLL_DELTA_Y * count;
scroll(target, x, y, smooth);
};
const scrollHorizonally = (count, smooth) => {
let target = scrollTarget();
let x = target.scrollLeft + SCROLL_DELTA_X * count;
let y = target.scrollTop;
scroll(target, x, y, smooth);
};
const scrollPages = (count, smooth) => {
let target = scrollTarget();
let height = target.clientHeight;
let x = target.scrollLeft;
let y = target.scrollTop + height * count;
scroll(target, x, y, smooth);
};
const scrollTop = (smooth) => {
let target = scrollTarget();
let x = target.scrollLeft;
let y = 0;
scroll(target, x, y, smooth);
};
const scrollBottom = (smooth) => {
let target = scrollTarget();
let x = target.scrollLeft;
let y = target.scrollHeight;
scroll(target, x, y, smooth);
};
const scrollHome = (smooth) => {
let target = scrollTarget();
let x = 0;
let y = target.scrollTop;
scroll(target, x, y, smooth);
};
const scrollEnd = (smooth) => {
let target = scrollTarget();
let x = target.scrollWidth;
let y = target.scrollTop;
scroll(target, x, y, smooth);
};
export {
scrollVertically, scrollHorizonally, scrollPages,
scrollTop, scrollBottom, scrollHome, scrollEnd
};
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