add day19

day19/src/lib/ReactiveObject.ts

@@ -0,0 +1,42 @@
+export class Reactive {
+	listeners: any;
+	contents: any;
+	constructor(obj: Record<string, unknown>) {
+		this.contents = obj;
+		this.listeners = {};
+		this.makeReactive(obj);
+	}
+
+	makeReactive(obj: Record<string, unknown>) {
+		Object.keys(obj).forEach(prop => this.makePropReactive(obj, prop));
+	}
+
+	makePropReactive(obj: Record<string, unknown>, key: string) {
+		let value = obj[key];
+
+		// Gotta be careful with this here
+		// eslint-disable-next-line @typescript-eslint/no-this-alias
+		const that = this;
+
+		Object.defineProperty(obj, key, {
+			get() {
+				return value;
+			},
+			set(newValue) {
+				value = newValue;
+				that.notify(key);
+			}
+		});
+	}
+
+	listen(prop: string, handler: any) {
+		if (!this.listeners[prop]) this.listeners[prop] = [];
+
+		this.listeners[prop].push(handler);
+	}
+
+	notify(prop: string) {
+		if (!this.listeners[prop]) return;
+		this.listeners[prop].forEach((listener: any) => listener(this.contents[prop]));
+	}
+}