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@lekoala
Created April 20, 2023 12:35
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/**
* Delegate listener to any events on any elements
* Set passive elements by default
* Avoid listening multiple times to the same event for the same handler
*/
const supportedPassiveTypes = [
"scroll",
"wheel",
"touchstart",
"touchmove",
"touchenter",
"touchend",
"touchleave",
"mouseout",
"mouseleave",
"mouseup",
"mousedown",
"mousemove",
"mouseenter",
"mousewheel",
"mouseover",
];
/**
* Store all listened selectors in here by type
* @type {Map<String, Map>}
*/
const map = new Map();
class Listener {
handleEvent(ev) {
const t = ev.target;
const selectors = map.get(ev.type);
if (t instanceof HTMLElement) {
// Leverage closest selector to match parent
// This is useful if you listen for example on a button with a nested svg icon that can be the actual target
for (const [s, h] of selectors) {
const closest = ev.target.closest(s);
if (closest) {
h(ev, closest); // also pass actual element as second param
}
}
}
}
}
let globalListener;
/**
* @callback EventCallback
* @param {Event} ev
* @param {HTMLElement} el
* @returns {void}
*/
/**
* @param {String} selector A selector that should work with .closest()
* @param {String|Array} type Event type or array of event types
* @param {EventCallback} listener A callback function
*/
function delegate(selector, type, listener) {
if (Array.isArray(type)) {
type.forEach((type) => {
delegate(selector, type, listener);
});
return;
}
if (!globalListener) {
globalListener = new Listener();
}
let listenerOptions = {
capture: true, //@link https://javascript.info/bubbling-and-capturing#capturing
};
// @link https://developer.chrome.com/docs/lighthouse/best-practices/uses-passive-event-listeners/
if (supportedPassiveTypes.includes(type)) {
listenerOptions.passive = true;
}
// need capture for most events, note that you cannot prevent events this way (with stopPropagation, preventDefault...)
document.addEventListener(type, globalListener, listenerOptions);
const listenerMap = map.get(type) ?? new Map();
if (listenerMap.size === 0) {
map.set(type, listenerMap);
}
listenerMap.set(selector, listener);
}
export default delegate;
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