framer-motion
Version:
A simple and powerful JavaScript animation library
50 lines (48 loc) • 1.8 kB
JavaScript
/**
* Map an IntersectionHandler callback to an element. We only ever make one handler for one
* element, so even though these handlers might all be triggered by different
* observers, we can keep them in the same map.
*/
const observerCallbacks = new WeakMap();
/**
* Multiple observers can be created for multiple element/document roots. Each with
* different settings. So here we store dictionaries of observers to each root,
* using serialised settings (threshold/margin) as lookup keys.
*/
const observers = new WeakMap();
const fireObserverCallback = (entry) => {
const callback = observerCallbacks.get(entry.target);
callback && callback(entry);
};
const fireAllObserverCallbacks = (entries) => {
entries.forEach(fireObserverCallback);
};
function initIntersectionObserver({ root, ...options }) {
const lookupRoot = root || document;
/**
* If we don't have an observer lookup map for this root, create one.
*/
if (!observers.has(lookupRoot)) {
observers.set(lookupRoot, {});
}
const rootObservers = observers.get(lookupRoot);
const key = JSON.stringify(options);
/**
* If we don't have an observer for this combination of root and settings,
* create one.
*/
if (!rootObservers[key]) {
rootObservers[key] = new IntersectionObserver(fireAllObserverCallbacks, { root, ...options });
}
return rootObservers[key];
}
function observeIntersection(element, options, callback) {
const rootInteresectionObserver = initIntersectionObserver(options);
observerCallbacks.set(element, callback);
rootInteresectionObserver.observe(element);
return () => {
observerCallbacks.delete(element);
rootInteresectionObserver.unobserve(element);
};
}
export { observeIntersection };