Add middleware example 3 for require json content

Author: mabelleeyanhwa

middleware_example_3.js

@@ -0,0 +1,29 @@
+const express = require("express");
+const app = express();
+const PORT = 3000;
+
+const requireJsonContent = (req, res, next) => {
+  if (req.headers["content-type"] !== "application/json") {
+    res.status(400).send("Server wants application/json!");
+  } else {
+    next();
+  }
+};
+
+app.post("/", requireJsonContent, (req, res, next) => {
+  res.send("Thanks for the JSON!");
+});
+
+app.get("/users", function(req, res) {
+  console.log("users list was shown");
+  res.send("Here is a list of users:....");
+});
+
+app.get("/books", function(req, res) {
+  console.log("books list was shown");
+  res.send("Here is a list of books:....");
+});
+
+const server = app.listen(PORT, () => {
+  console.log(`Server running at http://localhost:${PORT}`);
+});