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/**
* An event hub with a Vue instance like API
*
* NOTE: This is a derivative work from [mitt][1] v1.2.0 which is licensed by
* [MIT License][2] © [Jason Miller][3]
*
* [1]: https://github.com/developit/mitt
* [2]: https://opensource.org/licenses/MIT
* [3]: https://jasonformat.com/
*/
class EventHub {
constructor() {
this.$_all = new Map();
}
dispose() {
this.$_all.clear();
}
/**
* Register an event handler for the given type.
*
* @param {string|symbol} type Type of event to listen for
* @param {Function} handler Function to call in response to given event
*/
$on(type, handler) {
const handlers = this.$_all.get(type);
const added = handlers && handlers.push(handler);
if (!added) {
this.$_all.set(type, [handler]);
}
}
/**
* Remove an event handler or all handlers for the given type.
*
* @param {string|symbol} type Type of event to unregister `handler`
* @param {Function} handler Handler function to remove
*/
$off(type, handler) {
const handlers = this.$_all.get(type) || [];
const newHandlers = handler ? handlers.filter((x) => x !== handler) : [];
if (newHandlers.length) {
this.$_all.set(type, newHandlers);
} else {
this.$_all.delete(type);
}
}
/**
* Add an event listener to type but only trigger it once
*
* @param {string|symbol} type Type of event to listen for
* @param {Function} handler Handler function to call in response to event
*/
$once(type, handler) {
const wrapHandler = (...args) => {
this.$off(type, wrapHandler);
handler(...args);
};
this.$on(type, wrapHandler);
}
/**
* Invoke all handlers for the given type.
*
* @param {string|symbol} type The event type to invoke
* @param {Any} [evt] Any value passed to each handler
*/
$emit(type, ...args) {
const handlers = this.$_all.get(type) || [];
handlers.forEach((handler) => {
handler(...args);
});
}
}
/**
* Return a Vue like event hub
*
* - $on
* - $off
* - $once
* - $emit
*
* We'd like to shy away from using a full fledged Vue instance from this in the future.
*/
export default () => {
return new EventHub();
};
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