Add generic types and update tests (#107)

* Add generic types and update tests

* Add generic types to `on`, `off` and `emit` to enable some nicer TS
  usage if you specify what type you're expecting from the `EventData`.
* Move the tests to be TypeScript source. This will help catch errors in
  the tests if there are any type errors.
* Create a new test to test the generic types and make sure they pass
  and error when expected.
* Upgrade to Mocha 8.
* Did some tidying up of the package.json scripts.

* Tweak TS setup to validate tests

* Fix d.ts generation and tests

Co-authored-by: Jason Miller <[email protected]>

1 files changed, 7 insertions, 7 deletions

diff --git a/src/index.ts b/src/index.ts
index e640292..c681fd0 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -2,8 +2,8 @@ export type EventType = string | symbol;
 
 // An event handler can take an optional event argument
 // and should not return a value
-export type Handler = (event?: any) => void;
-export type WildcardHandler = (type: EventType, event?: any) => void
+export 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 type
 export type EventHandlerList = Array<Handler>;
@@ -13,10 +13,10 @@ export type WildCardEventHandlerList = Array<WildcardHandler>;
 export type EventHandlerMap = Map<EventType, EventHandlerList | WildCardEventHandlerList>;
 
 export interface Emitter {
-	on(type: EventType, handler: Handler): void;
+	on<T = any>(type: EventType, handler: Handler<T>): void;
 	on(type: '*', handler: WildcardHandler): void;
 
-	off(type: EventType, handler: Handler): void;
+	off<T = any>(type: EventType, handler: Handler<T>): void;
 	off(type: '*', handler: WildcardHandler): void;
 
 	emit<T = any>(type: EventType, event?: T): void;
@@ -38,7 +38,7 @@ export default function mitt(all?: EventHandlerMap): Emitter {
 		 * @param {Function} handler Function to call in response to given event
 		 * @memberOf mitt
 		 */
-		on(type: EventType, handler: Handler) {
+		on<T = any>(type: EventType, handler: Handler<T>) {
 			const handlers = all.get(type);
 			const added = handlers && handlers.push(handler);
 			if (!added) {
@@ -53,7 +53,7 @@ export default function mitt(all?: EventHandlerMap): Emitter {
 		 * @param {Function} handler Handler function to remove
 		 * @memberOf mitt
 		 */
-		off(type: EventType, handler: Handler) {
+		off<T = any>(type: EventType, handler: Handler<T>) {
 			const handlers = all.get(type);
 			if (handlers) {
 				handlers.splice(handlers.indexOf(handler) >>> 0, 1);
@@ -70,7 +70,7 @@ export default function mitt(all?: EventHandlerMap): Emitter {
 		 * @param {Any} [evt] Any value (object is recommended and powerful), passed to each handler
 		 * @memberOf mitt
 		 */
-		emit(type: EventType, evt: any) {
+		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); });
 		}