Implement AsyncEventEmitter

Co-Authored-By: Denys Otrishko <shishugi@gmail.com>
Co-Authored-By: Mykola Bilochub <nbelochub@gmail.com>
Co-Authored-By: Dmytro Nechai <nechaido@gmail.com>

.metadocrc

@@ -6,6 +6,7 @@
   "files": [
     "lib/adapters.js",
     "lib/array.js",
+    "lib/async-emitter.js",
     "lib/async-iterator.js",
     "lib/chain.js",
     "lib/collector.js",

README.md

@@ -301,6 +301,78 @@ Asynchronous some (iterate in series)
 
 Non-blocking synchronous map
 
+### class AsyncEmitter
+
+#### AsyncEmitter.prototype.constructor()
+
+#### AsyncEmitter.prototype.event(name)
+
+- `name`: [`<string>`][string] event name
+
+_Returns:_ { on: [`<Set>`][set], once: [`<Set>`][set] } }
+
+Get or create event
+
+#### AsyncEmitter.prototype.on(name, fn)
+
+- `name`: [`<string>`][string] event name
+- `fn`: [`<Function>`][function] listener
+
+Add listener
+
+#### AsyncEmitter.prototype.once(name, fn)
+
+- `name`: [`<string>`][string] event name
+- `fn`: [`<Function>`][function] listener
+
+_Returns:_ [`<Promise>`][promise]|[`<null>`][null]
+
+Add listener
+
+#### AsyncEmitter.prototype.emit(name, args)
+
+- `name`: [`<string>`][string] event name
+- `args`: `<any[]>`
+
+_Returns:_ [`<Promise>`][promise]|[`<null>`][null]
+
+Emit event
+
+#### AsyncEmitter.prototype.remove(name, fn)
+
+- `name`: [`<string>`][string] event name
+- `fn`: [`<Function>`][function] listener to remove
+
+Remove event listener
+
+#### AsyncEmitter.prototype.clear(name)
+
+- `name`: [`<string>`][string] event name
+
+Remove all listeners or by name
+
+#### AsyncEmitter.prototype.count(name)
+
+- `name`: [`<string>`][string] event name
+
+_Returns:_ [`<number>`][number]
+
+Get listeners count by event name
+
+#### AsyncEmitter.prototype.listeners(name)
+
+- `name`: [`<string>`][string] event name
+
+_Returns:_ [`<Function[]>`][function]
+
+Get listeners array by event name
+
+#### AsyncEmitter.prototype.names()
+
+_Returns:_ [`<string[]>`][string] names
+
+Get event names array
+
 ### asyncIter(base)
 
 - `base`: [`<Iterable>`][iterable]|[`<AsyncIterable>`][asynciterable] an
@@ -921,6 +993,7 @@ Set timeout for asynchronous function execution
 [object]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object
 [function]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function
 [promise]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise
+[set]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set
 [array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array
 [error]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error
 [boolean]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type

lib/async-emitter.js

@@ -0,0 +1,106 @@
+'use strict';
+
+class AsyncEmitter {
+  constructor() {
+    this.events = new Map();
+  }
+
+  // Get or create event
+  //   name <string> event name
+  // Returns: { on: <Set>, once: <Set> } }
+  event(name) {
+    const { events } = this;
+    const event = events.get(name);
+    if (event) return event;
+    const res = { on: new Set(), once: new Set() };
+    events.set(name, res);
+    return res;
+  }
+
+  // Add listener
+  //   name <string> event name
+  //   fn <Function> listener
+  on(name, fn) {
+    this.event(name).on.add(fn);
+  }
+
+  // Add listener
+  //   name <string> event name
+  //   fn <Function> listener
+  // Returns: <Promise> | <null>
+  once(name, fn) {
+    if (fn === undefined) {
+      return new Promise(resolve => {
+        this.once(name, resolve);
+      });
+    }
+    this.event(name).once.add(fn);
+    return null;
+  }
+
+  // Emit event
+  //   name <string> event name
+  //   args <any[]>
+  // Returns: <Promise> | <null>
+  emit(name, ...args) {
+    const { events } = this;
+    const event = events.get(name);
+    if (!event) return null;
+    const { on, once } = event;
+    const promises = [...on.values(), ...once.values()].map(fn => fn(...args));
+    once.clear();
+    if (on.size === 0) events.delete(name);
+    return Promise.all(promises);
+  }
+
+  // Remove event listener
+  //   name <string> event name
+  //   fn <Function> listener to remove
+  remove(name, fn) {
+    const { events } = this;
+    const event = events.get(name);
+    if (!event) return;
+    const { on, once } = event;
+    on.delete(fn);
+    once.delete(fn);
+    if (on.size === 0 && once.size === 0) {
+      events.delete(name);
+    }
+  }
+
+  // Remove all listeners or by name
+  //   name <string> event name
+  clear(name) {
+    const { events } = this;
+    if (!name) events.clear();
+    else events.delete(name);
+  }
+
+  // Get listeners count by event name
+  //   name <string> event name
+  // Returns: <number>
+  count(name) {
+    const event = this.events.get(name);
+    if (!event) return 0;
+    const { on, once } = event;
+    return on.size + once.size;
+  }
+
+  // Get listeners array by event name
+  //   name <string> event name
+  // Returns: <Function[]>
+  listeners(name) {
+    const event = this.events.get(name);
+    if (!event) return [];
+    const { on, once } = event;
+    return [...on.values(), ...once.values()];
+  }
+
+  // Get event names array
+  // Returns: <string[]> names
+  names() {
+    return [...this.events.keys()];
+  }
+}
+
+module.exports = { AsyncEmitter };

metasync.js

@@ -7,6 +7,7 @@ const submodules = [
   'composition', // Unified abstraction
   'adapters', // Adapters to convert different async contracts
   'array', // Array utilities
+  'async-emitter', // AsyncEmitter
   'chain', // Process arrays sync and async array in chain
   'collector', // DataCollector and KeyCollector
   'control', // Control flow utilities