feat: add on (#2)

src/interface.ts

@@ -6,7 +6,11 @@ export interface Listener<T = void> {
 
 /** Generic type for `onSomeEvent`, which is a function itself. */
 export interface IEvent<T = void> {
-  /** Adds listener, returns a dispose function. */
+  /**
+   * Adds a listener to the event.
+   * @param listener The callback to add.
+   * @returns A function to remove the listener.
+   */
   (listener: Listener<T>): () => void;
 }
 
@@ -17,14 +21,18 @@ export interface AddEventListener<T = void> extends IEvent<T> {
    */
   size(): number;
   /**
-   * Removes listener.
+   * Adds a listener to the event.
+   * @param listener The callback to add.
+   * @returns A function to remove the listener.
+   */
+  on(listener: Listener<T>): () => void;
+  /**
+   * Removes a listener from the event.
    * @param listener The callback to remove. If omitted, all listeners are removed.
    * @returns Whether the listener was found and removed.
    */
   off(listener?: Listener<T>): boolean;
-  /**
-   * Removes all listeners.
-   */
+
   dispose(): void;
 
   /**

src/internal/variants/set-lazy.ts

@@ -95,13 +95,10 @@ function dispose<T = void>(this: AddEventListenerImpl<T>): void {
  */
 export const event = <T = void>(): AddEventListener<T> => {
   function addEventListener(listener: Listener<T>): () => void {
-    on.call<AddEventListenerImpl<T>, [Listener<T>], void>(
-      addEventListener,
-      listener
-    );
-    return () => addEventListener.off(listener);
+    return addEventListener.on(listener);
   }
   addEventListener.size = size;
+  addEventListener.on = on;
   addEventListener.off = off;
   addEventListener.dispose = dispose;
   addEventListener[SEND] = send;

src/internal/variants/set-simple.ts

@@ -28,6 +28,14 @@ function size<T>(this: AddEventListenerImpl<T>): number {
   return this.listeners_.size;
 }
 
+function on<T>(
+  this: AddEventListenerImpl<T>,
+  listener: Listener<T>
+): () => void {
+  this.listeners_.add(listener);
+  return () => this.off(listener);
+}
+
 function off<T>(
   this: AddEventListenerImpl<T>,
   listener?: Listener<T>
@@ -63,11 +71,11 @@ function dispose<T>(this: AddEventListenerImpl<T>): void {
  */
 export const event = <T = void>(): AddEventListener<T> => {
   function addEventListener(listener: Listener<T>): () => void {
-    addEventListener.listeners_.add(listener);
-    return () => addEventListener.off(listener);
+    return addEventListener.on(listener);
   }
   addEventListener.listeners_ = new Set<Listener<T>>();
   addEventListener.size = size;
+  addEventListener.on = on;
   addEventListener.off = off;
   addEventListener.dispose = dispose;
   addEventListener[SEND] = send;

src/internal/variants/sparse-array-lazy.ts

@@ -111,14 +111,11 @@ function dispose<T = void>(this: AddEventListenerImpl<T>): void {
  */
 export const event = <T = void>(): AddEventListener<T> => {
   function addEventListener(listener: Listener<T>): () => void {
-    on.call<AddEventListenerImpl<T>, [Listener<T>], void>(
-      addEventListener,
-      listener
-    );
-    return () => addEventListener.off(listener);
+    return addEventListener.on(listener);
   }
   addEventListener.size_ = 0;
   addEventListener.size = size;
+  addEventListener.on = on;
   addEventListener.off = off;
   addEventListener.dispose = dispose;
   addEventListener[SEND] = send;