Create event-emitter.ts

Author: kamyu104

TypeScript/event-emitter.ts

@@ -0,0 +1,42 @@
+// Time:  subscribe:   O(1)
+//        unsubscribe: O(1)
+//        emit:        O(n)
+// Space: O(n)
+
+type Callback = (...args: any[]) => any;
+type Subscription = {
+    unsubscribe: () => void
+}
+
+class EventEmitter {
+    #lookup: Map<string, Callback[]>;
+    constructor() {
+        this.#lookup = new Map<string, Callback[]>();
+    }
+
+    subscribe(eventName: string, callback: Callback): Subscription {
+        if (!this.#lookup.has(eventName)) {
+            this.#lookup.set(eventName, []);
+        }
+        this.#lookup.get(eventName).push(callback);
+        return {
+            unsubscribe: () => {
+                const i = this.#lookup.get(eventName).indexOf(callback);
+                if (i !== -1) {
+                    this.#lookup.get(eventName).splice(i, 1);
+                }
+            }
+        };
+    }
+
+    emit(eventName: string, args: any[] = []): any {
+        if (!this.#lookup.has(eventName)) {
+            return [];
+        }
+        let result = [];
+        for (const listener of this.#lookup.get(eventName)) {
+            result.push(listener(...args));
+        }
+        return result;
+    }
+}