diff --git a/chapter04/src/get_parameters.js b/chapter04/src/get_parameters.js
new file mode 100644
index 0000000..1723425
--- /dev/null
+++ b/chapter04/src/get_parameters.js
@@ -0,0 +1,25 @@
+/* @flow */
+"use strict";
+
+const express = require("express");
+const app = express();
+
+const bodyParser = require("body-parser");
+app.use(bodyParser.urlencoded({extended:false}));
+
+app.use("/", (req, res) => {
+    console.log(req.query, req.body);
+    res.send("Server alive, with Express!");
+});
+
+// eslint-disable-next-line no-unused-vars
+app.use((err, req, res, next) => {
+    console.error("Error....", err.message);
+    res.status(500).send("INTERNAL SERVER ERROR");
+});
+
+app.listen(8080, () =>
+    console.log(
+        "Mini server (with Express) ready at http://localhost:8080/!"
+    )
+);
diff --git a/chapter04/src/middleware.js b/chapter04/src/middleware.js
new file mode 100644
index 0000000..862e7d6
--- /dev/null
+++ b/chapter04/src/middleware.js
@@ -0,0 +1,30 @@
+/* @flow */
+"use strict";
+
+const express = require("express");
+const app = express();
+
+app.use((req, res, next) => {
+    console.log("Logger... ", new Date(), req.method, req.path);
+    next();
+});
+
+app.use((req, res, next) => {
+    if (req.method === "DELETE") {
+        next(new Error("DELETEs are not accepted!"));
+    } else {
+        res.send("Server alive, with Express!");
+    }
+});
+
+// eslint-disable-next-line no-unused-vars
+app.use((err, req, res, next) => {
+    console.error("Error....", err.message);
+    res.status(500).send("INTERNAL SERVER ERROR");
+});
+
+app.listen(8080, () =>
+    console.log(
+        "Mini server (with Express) ready at http://localhost:8080/!"
+    )
+);
diff --git a/chapter04/src/serve_statics_alt.js b/chapter04/src/serve_statics_alt.js
index 6da3d8c..b890622 100644
--- a/chapter04/src/serve_statics_alt.js
+++ b/chapter04/src/serve_statics_alt.js
@@ -20,6 +20,11 @@ app.get("/license", (req, res) =>
     res.sendFile(`${flagsPath}/license.txt`)
 );
 
+app.use((err, req, res, next) => {
+    console.error("Error....", err.message);
+    res.status(500).send("INTERNAL SERVER ERROR");
+});
+
 app.listen(8080, () =>
     console.log(
         "Mini Express static server ready at http://localhost:8080/!"