mitt.ts
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/**
* Mitt: Tiny functional event emitter / pubsub
*
* @name mitt
* @param {Array} [all] Optional array of event names to registered handler functions
* @returns {Function} The function's instance
*/
export default class Mitt {
private cache: Map<string | Symbol, Array<(...data: any) => void>>;
constructor(all = []) {
// A Map of event names to registered handler functions.
this.cache = new Map(all);
}
once(type: string | Symbol, handler: Fn) {
const decor = (...args: any[]) => {
handler && handler.apply(this, args);
this.off(type, decor);
};
this.on(type, decor);
return this;
}
/**
* Register an event handler for the given type.
*
* @param {string|symbol} type Type of event to listen for, or `"*"` for all events
* @param {Function} handler Function to call in response to given event
*/
on(type: string | Symbol, handler: Fn) {
const handlers = this.cache?.get(type);
const added = handlers && handlers.push(handler);
if (!added) {
this.cache.set(type, [handler]);
}
}
/**
* Remove an event handler for the given type.
*
* @param {string|symbol} type Type of event to unregister `handler` from, or `"*"`
* @param {Function} handler Handler function to remove
*/
off(type: string | Symbol, handler: Fn) {
const handlers = this.cache.get(type);
if (handlers) {
handlers.splice(handlers.indexOf(handler) >>> 0, 1);
}
}
/**
* Invoke all handlers for the given type.
* If present, `"*"` handlers are invoked after type-matched handlers.
*
* Note: Manually firing "*" handlers is not supported.
*
* @param {string|symbol} type The event type to invoke
* @param {*} [evt] Any value (object is recommended and powerful), passed to each handler
*/
emit(type: string | Symbol, evt?: any) {
for (const handler of (this.cache.get(type) || []).slice()) handler(evt);
for (const handler of (this.cache.get('*') || []).slice()) handler(type, evt);
}
/**
* Remove all event handlers.
*
* Note: This will also remove event handlers passed via `mitt(all: EventHandlerMap)`.
*/
clear() {
this.cache.clear();
}
}