20 new API endpoints

src/routes/api/array/average.js

@@ -0,0 +1,11 @@
+const express = require('express');
+const router = express.Router();
+
+router.post('/', (req, res) => {
+    const { input } = req.body;
+    if (!Array.isArray(input) || input.length === 0)
+        return res.status(400).json({ error: 'input must be a non-empty array' });
+    res.json({ ret: input.reduce((acc, n) => acc + Number(n), 0) / input.length });
+});
+
+module.exports = router;