Move emitter into model

source/Model/Emitter.ts

@@ -0,0 +1,104 @@
+export type EventType = string | symbol;
+
+// An event handler can take an optional event argument
+// and should not return a value
+export type Handler<T = any> = (event: T) => void;
+
+// An array of all currently registered event handlers for a type
+export type EventHandlerList<T = any> = Array<Handler<T>>;
+
+// A map of event types and their corresponding event handlers.
+export type EventHandlerMap<Events extends Record<EventType, any>> = Map<
+	keyof Events,
+	EventHandlerList<Events[keyof Events]>
+>;
+
+// Emitter function type
+type IEmitParamType<E extends Record<EventType, any>, K extends keyof E> = 
+	E[K] extends ( undefined | void ) ? [type: K] : [type: K, evt: E[K]];
+
+// Mixin to event object
+export type EventMixin<A extends Record<EventType, any>, B extends Record<EventType, any>> = {
+	[P in (keyof A | keyof B)] :
+		P extends (keyof A & keyof B) ? 
+			A[P] : 
+			P extends keyof A ? 
+				A[P] : 
+				P extends keyof B ? B[P] : 
+			never;
+}
+
+export class Emitter<Events extends Record<EventType, any>> {
+	
+	/**
+	 * A Map of event names to registered handler functions.
+	 */
+	public all: EventHandlerMap<Events>;
+
+	public constructor() {
+		this.all = new Map();
+	}
+
+	public resetAll() {
+		this.all = new Map();
+	}
+
+	public reset<Key extends keyof Events>(type: Key) {
+		this.all!.set(type, [] as EventHandlerList<Events[keyof Events]>);
+	}
+
+	/**
+	 * 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
+	 * @memberOf mitt
+	 */
+	public on<Key extends keyof Events>(type: Key, handler: Handler<Events[Key]>) {
+		const handlers: Array<Handler<Events[Key]>> | undefined = this.all!.get(type);
+		if (handlers) {
+			handlers.push(handler);
+		}
+		else {
+			this.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
+	 * @param {Function} [handler] Handler function to remove
+	 * @memberOf mitt
+	 */
+	public off<Key extends keyof Events>(type: Key, handler?: Handler<Events[Key]>) {
+		const handlers: Array<Handler<Events[Key]>> | undefined = this.all!.get(type);
+		if (handlers) {
+			if (handler) {
+				handlers.splice(handlers.indexOf(handler) >>> 0, 1);
+			}
+			else {
+				this.all!.set(type, []);
+			}
+		}
+	}
+
+	/**
+	 * Invoke all handlers for the given type.
+	 *
+	 * @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
+	 */
+	public emit<Key extends keyof Events>(...param: IEmitParamType<Events, Key>): this {
+		const [ type, evt ] = param;
+		let handlers = this.all!.get(type);
+		if (handlers) {
+			(handlers as EventHandlerList<Events[keyof Events]>)
+				.slice()
+				.map((handler) => {
+					handler(evt!);
+				});
+		}
+		return this;
+	}
+}