Add dinosaur API error handler

lecture_5/dinosaurs/src/app.js

@@ -1,9 +1,12 @@
 import express from "express";
 import { dinosaurRouter } from "./routes/dinosaurRoutes.js";
+import { errorHandler } from "./validation/errorHandler.js";
 
 const app = express();
 
 app.use(express.json());
 app.use(dinosaurRouter);
+// Error middleware must be registered after routes so it can handle rejected route handlers.
+app.use(errorHandler);
 
 export { app };

lecture_5/dinosaurs/src/validation/errorHandler.js

@@ -0,0 +1,17 @@
+import { ZodError } from "zod";
+
+// Centralized Express error middleware for validation and unexpected runtime errors.
+export const errorHandler = (error, _request, response, _next) => {
+	console.error(error);
+
+	if (error instanceof ZodError) {
+		return response.status(400).json({
+			message: "Validation error",
+			errors: error.issues,
+		});
+	}
+
+	return response.status(500).json({
+		message: "Internal server error",
+	});
+};