export type EventType = string | symbol;// An event handler can take an optional event argument// and should not return a valueexport type Handler<T = any> = (event?: T) => void;export type WildcardHandler = (type: EventType, event?: any) => void;// An array of all currently registered event handlers for a typeexport type EventHandlerList = Array<Handler>;export type WildCardEventHandlerList = Array<WildcardHandler>;// A map of event types and their corresponding event handlers.export type EventHandlerMap = Map<EventType, EventHandlerList | WildCardEventHandlerList>;export interface Emitter { all: EventHandlerMap; on<T = any>(type: EventType, handler: Handler<T>): void; on(type: '*', handler: WildcardHandler): void; off<T = any>(type: EventType, handler: Handler<T>): void; off(type: '*', handler: WildcardHandler): void; emit<T = any>(type: EventType, event?: T): void; emit(type: '*', event?: any): void;
/** * 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 * @memberOf mitt */ on<T = any>(type: EventType, handler: Handler<T>) { const handlers = all?.get(type); const added = handlers && handlers.push(handler); if (!added) { all?.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 * @memberOf mitt */ off<T = any>(type: EventType, handler: Handler<T>) { const handlers = all?.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 {Any} [evt] Any value (object is recommended and powerful), passed to each handler * @memberOf mitt */ emit<T = any>(type: EventType, evt: T) { ((all?.get(type) || []) as EventHandlerList).slice().map((handler) => { handler(evt); }); ((all?.get('*') || []) as WildCardEventHandlerList).slice().map((handler) => { handler(type, evt); }); },