Refactor '/info' route to use reusable validation middleware and improve code readability

Author: eyuell21

Off-the-shelf middleware/script.js

@@ -1,40 +1,58 @@
 import express from 'express';
+
 const app = express();
+const PORT = 3000;
 
-// Built-in middleware to parse JSON bodies
+// Parse JSON bodies(built-in)
 app.use(express.json());
 
-// Middleware 1: Extract username from header or set to null
+// Middleware1,  Extract username from header
 function usernameMiddleware(req, res, next) {
   const username = req.header('X-Username');
   req.username = username || null;
   next();
 }
 
-app.post('/info', usernameMiddleware, function(req, res) {
-  // req.body is now automatically parsed by express.json()
-  if (
-    !Array.isArray(req.body) ||
-    !req.body.every(function(item) { return typeof item === 'string'; })
-  ) {
-    return res.status(400).send('Invalid body: must be JSON array of strings');
-  }
 
-  const authMessage = req.username
-    ? 'You are authenticated as ' + req.username + '.'
-    : 'You are not authenticated.';
+//Reusable validator 
+function validateArrayOf(type) {
+  return function (req, res, next) {
+    if (
+      !Array.isArray(req.body) ||
+      !req.body.every(item => typeof item === type)
+    ) {
+      return res
+        .status(400)
+        .send(`Invalid body: must be JSON array of ${type}s`);
+    }
 
-  const count = req.body.length;
-  const subjects = req.body.join(', ');
-  const subjectWord = count === 1 ? 'subject' : 'subjects';
-  const subjectMessage = count
-    ? 'You have requested information about ' + count + ' ' + subjectWord + ': ' + subjects + '.'
-    : 'You have requested information about 0 subjects.';
+    next();
+  };
+}
 
-  res.send(authMessage + '\n\n' + subjectMessage);
-});
+// Route
 
-const PORT = 3000;
-app.listen(PORT, function() {
-  console.log('Server running on http://localhost:' + PORT);
-});
+app.post(
+  '/info',
+  usernameMiddleware,
+  validateArrayOf('string'),
+  (req, res) => {
+    const authMessage = req.username
+      ? `You are authenticated as ${req.username}.`
+      : 'You are not authenticated.';
+
+    const count = req.body.length;
+    const subjects = req.body.join(', ');
+    const subjectWord = count === 1 ? 'subject' : 'subjects';
+
+    const subjectMessage = count
+      ? `You have requested information about ${count} ${subjectWord}: ${subjects}.`
+      : 'You have requested information about 0 subjects.';
+
+    res.send(`${authMessage}\n\n${subjectMessage}`);
+  }
+);
+
+app.listen(PORT, () => {
+  console.log(`Server running on http://localhost:${PORT}`);
+});