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export type EventType = string | symbol;
// An event handler can take an optional event argument
// and should not return a value
export type Handler<T = unknown> = (event: T) => void;
export type WildcardHandler<T = Record<string, unknown>> = (
type: keyof T,
event: T[keyof T]
) => void;
// An array of all currently registered event handlers for a type
export type EventHandlerList<T = unknown> = Array<Handler<T>>;
export type WildCardEventHandlerList<T = Record<string, unknown>> = Array<
WildcardHandler<T>
>;
// A map of event types and their corresponding event handlers.
export type EventHandlerMap<Events extends Record<EventType, unknown>> = Map<
keyof Events | '*',
EventHandlerList<Events[keyof Events]> | WildCardEventHandlerList<Events>
>;
export interface Emitter<Events extends Record<EventType, unknown>> {
all: EventHandlerMap<Events>;
on<Key extends keyof Events>(type: Key, handler: Handler<Events[Key]>): void;
on(type: '*', handler: WildcardHandler<Events>): void;
once<Key extends keyof Events>(type: Key, handler: Handler<Events[Key]>): void;
once(type: '*', handler: WildcardHandler<Events>): void;
off<Key extends keyof Events>(
type: Key,
handler?: Handler<Events[Key]>
): void;
off(type: '*', handler: WildcardHandler<Events>): void;
emit<Key extends keyof Events>(type: Key, event: Events[Key]): void;
emit<Key extends keyof Events>(
type: undefined extends Events[Key] ? Key : never
): void;
when<Key extends keyof Events>(type: Key): Promise<void>;
}
/**
* Nitt: Tiny (~200b) functional event emitter / pubsub.
* @name nitt
* @returns {Nitt}
*/
export default function nitt<Events extends Record<EventType, unknown>>(
all?: EventHandlerMap<Events>
): Emitter<Events> {
type GenericEventHandler =
| Handler<Events[keyof Events]>
| WildcardHandler<Events>;
all = all || new Map();
return {
/**
* A Map of event names to registered handler functions.
*/
all,
/**
* 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 nitt
*/
on<Key extends keyof Events>(type: Key, handler: GenericEventHandler) {
const handlers: Array<GenericEventHandler> | undefined = all!.get(type);
if (handlers) {
handlers.push(handler);
} else {
all!.set(type, [handler] as EventHandlerList<Events[keyof Events]>);
}
},
/**
* Remove an event handler for the given type.
* If `handler` is omitted, all handlers of the given type are removed.
* @param {string|symbol} type Type of event to unregister `handler` from (`'*'` to remove a wildcard handler)
* @param {Function} [handler] Handler function to remove
* @memberOf nitt
*/
off<Key extends keyof Events>(type: Key, handler?: GenericEventHandler) {
const handlers: Array<GenericEventHandler> | undefined = all!.get(type);
if (handlers) {
if (handler) {
handlers.splice(handlers.indexOf(handler) >>> 0, 1);
} else {
all!.set(type, []);
}
}
},
/**
* 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 nitt
*/
emit<Key extends keyof Events>(type: Key, evt?: Events[Key]) {
let handlers = all!.get(type);
if (handlers) {
(handlers as EventHandlerList<Events[keyof Events]>)
.slice()
.map((handler) => {
handler(evt!);
});
}
handlers = all!.get('*');
if (handlers) {
(handlers as WildCardEventHandlerList<Events>)
.slice()
.map((handler) => {
handler(type, evt!);
});
}
},
/**
* Register an event handler that is executed just once 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 nitt
*/
once<Key extends keyof Events>(type: Key, handler: GenericEventHandler) {
if (type === '*') {
const onceHandler: WildcardHandler<Events> = (type: keyof Events, event: Events[keyof Events]) => {
(handler as WildcardHandler<Events>)(type, event);
this.off('*', onceHandler);
};
this.on('*', onceHandler);
} else {
const onceHandler = (evt: Events[Key]) => {
(handler as Handler<Events[Key]>)(evt);
this.off(type, onceHandler);
};
this.on(type, onceHandler);
}
},
/**
* Returns a promise for a single event
*
* @param {String} type Type of event to listen for, or `"*"` for any event
* @returns {Promise<any>}
*/
when<Key extends keyof Events>(type: Key): Promise<any> {
return new Promise((resolve: GenericEventHandler) => {
if (type === '*') {
this.once('*', (resolve as WildcardHandler<Events>));
} else {
this.once(type, (resolve as Handler<Events[Key]>));
}
});
}
};
}
|
