Add draft of TypeScript typesafe event emitter post

code/typescript-emitter/js1.js

@@ -0,0 +1,23 @@
+class EventEmitter {
+    constructor() {
+        this.handlers = {}
+    }
+
+    emit(event) {
+        this.handlers[event]?.forEach(h => h());
+    }
+
+    addHandler(event, handler) {
+        if(!this.handlers[event]) {
+            this.handlers[event] = [handler];
+        } else {
+            this.handlers[event].push(handler);
+        }
+    }
+}
+
+const emitter = new EventEmitter();
+emitter.addHandler("start", () => console.log("Started!"));
+emitter.addHandler("end", () => console.log("Ended!"));
+emitter.emit("end");
+emitter.emit("start");

code/typescript-emitter/js2.js

@@ -0,0 +1,23 @@
+class EventEmitter {
+    constructor() {
+        this.handlers = {}
+    }
+
+    emit(event, value) {
+        this.handlers[event]?.forEach(h => h(value));
+    }
+
+    addHandler(event, handler) {
+        if(!this.handlers[event]) {
+            this.handlers[event] = [handler];
+        } else {
+            this.handlers[event].push(handler);
+        }
+    }
+}
+
+const emitter = new EventEmitter();
+emitter.addHandler("numberChange", n => console.log("New number value is: ", n));
+emitter.addHandler("stringChange", s => console.log("New string value is: ", s));
+emitter.emit("numberChange", 1);
+emitter.emit("stringChange", "3");

code/typescript-emitter/ts.ts

@@ -0,0 +1,27 @@
+class EventEmitter<T> {
+    private handlers: { [eventName in keyof T]?: ((value: T[eventName]) => void)[] }
+
+    constructor() {
+        this.handlers = {}
+    }
+
+    emit<K extends keyof T>(event: K, value: T[K]): void {
+        this.handlers[event]?.forEach(h => h(value));
+    }
+
+    addHandler<K extends keyof T>(event: K, handler: (value: T[K]) => void): void {
+        if(!this.handlers[event]) {
+            this.handlers[event] = [handler];
+        } else {
+            this.handlers[event].push(handler);
+        }
+    }
+}
+
+const emitter = new EventEmitter<{ numberChange: number, stringChange: string }>();
+emitter.addHandler("numberChange", n => console.log("New number value is: ", n));
+emitter.addHandler("stringChange", s => console.log("New string value is: ", s));
+emitter.emit("numberChange", 1);
+emitter.emit("stringChange", "3");
+emitter.emit("numberChange", "1");
+emitter.emit("stringChange", 3);