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