Add solution #2694

Author: JoshCrozier

2694-event-emitter.js

@@ -0,0 +1,66 @@
+/**
+ * 2694. Event Emitter
+ * https://leetcode.com/problems/event-emitter/
+ * Difficulty: Medium
+ *
+ * Design an EventEmitter class. This interface is similar (but with some differences) to the one
+ * found in Node.js or the Event Target interface of the DOM. The EventEmitter should allow for
+ * subscribing to events and emitting them.
+ *
+ * Your EventEmitter class should have the following two methods:
+ * - subscribe - This method takes in two arguments: the name of an event as a string and a callback
+ *   function. This callback function will later be called when the event is emitted.
+ *   An event should be able to have multiple listeners for the same event. When emitting an event
+ *   with multiple callbacks, each should be called in the order in which they were subscribed.
+ *   An array of results should be returned. You can assume no callbacks passed to subscribe are
+ *   referentially identical.
+ *   The subscribe method should also return an object with an unsubscribe method that enables the
+ *   user to unsubscribe. When it is called, the callback should be removed from the list of
+ *   subscriptions and undefined should be returned.
+ * - emit - This method takes in two arguments: the name of an event as a string and an optional
+ *   array of arguments that will be passed to the callback(s). If there are no callbacks subscribed
+ *   to the given event, return an empty array. Otherwise, return an array of the results of all
+ *   callback calls in the order they were subscribed.
+ */
+
+class EventEmitter {
+  constructor() {
+    this.events = new Map();
+  }
+
+  /**
+   * @param {string} eventName
+   * @param {Function} callback
+   * @return {Object}
+   */
+  subscribe(eventName, callback) {
+    if (!this.events.has(eventName)) {
+      this.events.set(eventName, []);
+    }
+
+    const listeners = this.events.get(eventName);
+    listeners.push(callback);
+
+    return {
+      unsubscribe: () => {
+        const index = listeners.indexOf(callback);
+        if (index !== -1) {
+          listeners.splice(index, 1);
+        }
+      }
+    };
+  }
+
+  /**
+   * @param {string} eventName
+   * @param {Array} args
+   * @return {Array}
+   */
+  emit(eventName, args = []) {
+    if (!this.events.has(eventName)) {
+      return [];
+    }
+
+    return this.events.get(eventName).map(listener => listener(...args));
+  }
+}

README.md

@@ -478,6 +478,7 @@
 2677|[Chunk Array](./2677-chunk-array.js)|Easy|
 2683|[Neighboring Bitwise XOR](./2683-neighboring-bitwise-xor.js)|Medium|
 2693|[Call Function with Custom Context](./2693-call-function-with-custom-context.js)|Medium|
+2694|[Event Emitter](./2694-event-emitter.js)|Medium|
 2695|[Array Wrapper](./2695-array-wrapper.js)|Easy|
 2703|[Return Length of Arguments Passed](./2703-return-length-of-arguments-passed.js)|Easy|
 2704|[To Be Or Not To Be](./2704-to-be-or-not-to-be.js)|Easy|