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/**
* Provides means to hook into the scroll event. Registered callbacks are
* called with the current scroll top and scroll left position so both
* vertical and horizontal scroll events can be handled.
*
* Updates/calls to the callback are synchronized to screen refresh by using
* the animation frame method (which will fallback to a timer based solution).
*/
const handlers = {};
let animId = false;
let lastTop = null;
let lastLeft = null;
function refresh() {
const hasHandlers = Object.keys(handlers).length > 0;
if (!hasHandlers && animId !== false) {
window.cancelAnimationFrame(animId);
animId = false;
} else if (hasHandlers && animId === false) {
animId = window.requestAnimationFrame(() => Scroll.executeHandlers());
}
}
function engageScrollTrigger() {
window.removeEventListener('scroll', refresh);
window.addEventListener('scroll', refresh, {once: true});
}
const Scroll = {
executeHandlers(only_these = []) {
const scrollTop = document.scrollingElement.scrollTop;
const scrollLeft = document.scrollingElement.scrollLeft;
if (scrollTop !== lastTop || scrollLeft !== lastLeft) {
for (const [index, handler] of Object.entries(handlers)) {
if (only_these.length === 0 || only_these.includes(index)) {
handler(scrollTop, scrollLeft);
}
}
lastTop = scrollTop;
lastLeft = scrollLeft;
}
animId = false;
engageScrollTrigger();
},
addHandler(index, handler, immediate = false) {
handlers[index] = handler;
engageScrollTrigger();
if (immediate) {
Scroll.executeHandlers([index]);
}
},
removeHandler(index) {
delete handlers[index];
engageScrollTrigger();
}
};
export default Scroll;
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