Add route for Fibonacci function

src/fibRoute.ts

@@ -1,16 +1,21 @@
-// Endpoint for querying the fibonacci numbers
+// Endpoint for querying the fibonacci numbers.
+import { Request, Response } from 'express';
+import { fibonacci } from './fib';
 
-const fibonacci = require("./fib");
+export default function fibonacciHandler(req: Request, res: Response): void {
+  const numStr: string = req.params.num;
+  const num: number = parseInt(numStr, 10);
 
-export default (req, res) => {
-  const { num } = req.params;
-
-  const fibN = fibonacci(parseInt(num));
-  let result = `fibonacci(${num}) is ${fibN}`;
-
-  if (fibN < 0) {
-    result = `fibonacci(${num}) is undefined`;
+  // Check if the parsed number is valid
+  if (isNaN(num)) {
+    res.status(400).send('Invalid number provided');
+    return;
   }
 
+  const fibN: number = fibonacci(num);
+  const result: string = fibN < 0 
+    ? fibonacci(${num}) is undefined
+    : fibonacci(${num}) is ${fibN};
+
   res.send(result);
-};
+}