Add support for mitt.off("type"), which removes all handlers of a giv…

…en type

README.md

@@ -140,12 +140,12 @@ Register an event handler for the given type.
 ### off
 
 Remove an event handler for the given type.
-If omit the `handler`, all event handlers of the given type are deleted.
+If `handler` is omitted, all handlers of the given type are removed.
 
 #### Parameters
 
 -   `type` **([string](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String) \| [symbol](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Symbol))** Type of event to unregister `handler` from, or `'*'`
--   `handler` **[Function](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Statements/function)** Handler function to remove
+-   `handler` **[Function](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Statements/function)?** Handler function to remove
 
 ### emit
 

src/index.ts

@@ -59,8 +59,10 @@ export default function mitt<Events extends Record<EventType, unknown>>(
 		 */
 		on<Key extends keyof Events>(type: Key, handler: GenericEventHandler) {
 			const handlers: Array<GenericEventHandler> | undefined = all!.get(type);
-			const added = handlers && handlers.push(handler);
-			if (!added) {
+			if (handlers) {
+				handlers.push(handler);
+			}
+			else {
 				all!.set(type, [handler] as EventHandlerList<Events[keyof Events]>);
 			}
 		},
@@ -79,7 +81,7 @@ export default function mitt<Events extends Record<EventType, unknown>>(
 					handlers.splice(handlers.indexOf(handler) >>> 0, 1);
 				}
 				else {
-					all.delete(type);
+					all!.set(type, []);
 				}
 			}
 		},