diff --git a/chapter01/.flowconfig b/chapter01/.flowconfig
new file mode 100644
index 0000000..1fed445
--- /dev/null
+++ b/chapter01/.flowconfig
@@ -0,0 +1,11 @@
+[ignore]
+
+[include]
+
+[libs]
+
+[lints]
+
+[options]
+
+[strict]
diff --git a/chapter02/.flowconfig b/chapter02/.flowconfig
new file mode 100644
index 0000000..1fed445
--- /dev/null
+++ b/chapter02/.flowconfig
@@ -0,0 +1,11 @@
+[ignore]
+
+[include]
+
+[libs]
+
+[lints]
+
+[options]
+
+[strict]
diff --git a/chapter02/package.json b/chapter02/package.json
index 4c4bbc2..082b897 100644
--- a/chapter02/package.json
+++ b/chapter02/package.json
@@ -26,7 +26,7 @@
             "node": true
         },
         "extends": ["eslint:recommended", "plugin:flowtype/recommended"],
-        "plugins": ["flowtype"],
+        "plugins": ["babel", "flowtype"],
         "rules": {
             "no-console": "off"
         }
diff --git a/chapter02/src/extdate.js b/chapter02/src/extdate.js
index 8c6a0e0..efa69a6 100644
--- a/chapter02/src/extdate.js
+++ b/chapter02/src/extdate.js
@@ -1,3 +1,5 @@
+// @flow
+
 class ExtDate extends Date {
     fullDate() {
         const months = [
@@ -16,7 +18,7 @@ class ExtDate extends Date {
         ];
 
         return (
-            months[this.getMonth()] + 
+            months[this.getMonth()] +
             " " +
             String(this.getDate()).padStart(2, "0") +
             " " +
@@ -41,7 +43,7 @@ class ExtDate extends Date {
         ];
         return months[m];
     }
-    
+
     fullDate2() {
         return (
             ExtDate.getMonthName(this.getMonth()) +
@@ -55,5 +57,5 @@ class ExtDate extends Date {
 
 console.log(new ExtDate().fullDate()); // "MAY 01 2018"
 
-console.log(ExtDate.getMonthName(8));  // "SEP"
+console.log(ExtDate.getMonthName(8)); // "SEP"
 console.log(new ExtDate().fullDate2()); // "MAY 01 2018"
diff --git a/chapter02/src/persons.js b/chapter02/src/persons.js
index f2b551d..ced1e26 100644
--- a/chapter02/src/persons.js
+++ b/chapter02/src/persons.js
@@ -24,7 +24,7 @@ class Person {
     }
 }
 
-pp = new Person("Erika", "Mustermann");
+let pp = new Person("Erika", "Mustermann");
 console.log(pp); // Person {first: "Erika", last: "Mustermann"}
 console.log(pp.initials()); // "EM"
 console.log(pp.fullName()); // "Erika Mustermann"
@@ -44,7 +44,7 @@ class Developer extends Person {
     }
 }
 
-window.dd = new Developer("John", "Doe", "JS");
+let dd = new Developer("John", "Doe", "JS");
 console.log(dd); // Developer {first: "John", last: "Doe", language: "JS"}
 console.log(dd.initials()); // "JD"
 console.log(dd.fullName()); // "John Doe, JS dev"
@@ -63,68 +63,64 @@ const countKeysMixin = base =>
         }
     };
 
-    class PersonWithTwoMixins extends toJsonMixin(countKeysMixin(Person)) {
-        toJson() { 
-            // redefine the method, just for the sake of it
-             return "NEW TOJSON " + super.toJson();
-        }
+class PersonWithTwoMixins extends toJsonMixin(countKeysMixin(Person)) {
+    toJson() {
+        // redefine the method, just for the sake of it
+        return "NEW TOJSON " + super.toJson();
+    }
+}
+
+let p2m = new PersonWithTwoMixins("Jane", "Roe");
+console.log(p2m);
+console.log(p2m.toJson()); // NEW TOJSON {"first":"Jane","last":"Roe"}
+console.log(p2m.countKeys()); // 2
+
+class ExtDate extends Date {
+    fullDate() {
+        const months = [
+            "JAN",
+            "FEB",
+            "MAR",
+            "APR",
+            "MAY",
+            "JUN",
+            "JUL",
+            "AUG",
+            "SEP",
+            "OCT",
+            "NOV",
+            "DEC"
+        ];
+
+        return (
+            months[this.getMonth()] +
+            " " +
+            String(this.getDate()).padStart(2, "0") +
+            " " +
+            this.getFullYear()
+        );
     }
 
-    
-    p2m = new PersonWithTwoMixins("Jane", "Roe");
-    console.log(p2m);
-    console.log(p2m.toJson());    // NEW TOJSON {"first":"Jane","last":"Roe"}
-    console.log(p2m.countKeys()); // 2
-
-
-
-    class ExtDate extends Date {
-        fullDate() {
-            const months = [
-                "JAN",
-                "FEB",
-                "MAR",
-                "APR",
-                "MAY",
-                "JUN",
-                "JUL",
-                "AUG",
-                "SEP",
-                "OCT",
-                "NOV",
-                "DEC"
-            ];
-    
-            return (
-                months[this.getMonth()] + 
-                " " +
-                String(this.getDate()).padStart(2, "0") +
-                " " +
-                this.getFullYear()
-            );
-        }
-    
-    
-        static getMonthName(m) {
-            const months = [
-                "JAN",
-                "FEB",
-                // etc...
-                "NOV",
-                "DEC"
-            ];
-            return months[m];
-        }
-    
-        fullDate2() {
-            return (
-                ExtDate.getMonthName(this.getMonth()) +
-                " " +
-                String(this.getDate()).padStart(2, "0") +
-                " " +
-                this.getFullYear()
-            );
-        }
+    static getMonthName(m) {
+        const months = [
+            "JAN",
+            "FEB",
+            // etc...
+            "NOV",
+            "DEC"
+        ];
+        return months[m];
     }
-    
-    console.log(new ExtDate().fullDate()); // "MAY 01 2018"
\ No newline at end of file
+
+    fullDate2() {
+        return (
+            ExtDate.getMonthName(this.getMonth()) +
+            " " +
+            String(this.getDate()).padStart(2, "0") +
+            " " +
+            this.getFullYear()
+        );
+    }
+}
+
+console.log(new ExtDate().fullDate()); // "MAY 01 2018"
diff --git a/chapter02/src/types_advanced.js b/chapter02/src/types_advanced.js
new file mode 100644
index 0000000..c760184
--- /dev/null
+++ b/chapter02/src/types_advanced.js
@@ -0,0 +1,19 @@
+/* @flow */
+/* eslint-disable no-unused-vars */
+
+let flag: number | boolean;
+flag = true; // OK
+flag = 1; // also OK
+flag = "1"; // error: wrong type
+
+let traffic: "red" | "amber" | "green"; // traffic is implicitly string
+traffic = "yellow"; // error: not allowed
+
+type numberOrString = number | string;
+
+function addTwo(x: numberOrString, y: numberOrString) {
+    return x + y;
+}
+
+const fs: any = require("fs");
+fs.readFile("/somefilename.ext", processData);
diff --git a/chapter02/src/types_basic.js b/chapter02/src/types_basic.js
new file mode 100644
index 0000000..8cc533c
--- /dev/null
+++ b/chapter02/src/types_basic.js
@@ -0,0 +1,33 @@
+/* @flow */
+/* eslint-disable no-unused-vars */
+
+let someFlag: boolean;
+let greatTotal: number;
+let firstName: string;
+
+function toString(x: number): string {
+    return String(x);
+}
+
+function addTwo(x: number | string, y: number | string) {
+    return x + y;
+}
+
+function showValue(z: mixed): void {
+    // not returning anything
+    console.log("Showing... ", z);
+}
+
+let numbersList: Array<number>;
+numbersList = [22, 9, 60]; // OK
+numbersList[1] = "SEP"; // error; cannot assign a string to a number
+
+let anotherList: number[];
+
+let sealedObject: { name: string, age?: number };
+sealedObject.name = "Ivan Horvat"; // OK
+sealedObject.id = 229; // error: key isn't defined in the data type
+sealedObject = { age: 57 }; // error: mandatory field is missing
+
+let unsealedObject = {};
+unsealedObject.id = 229; // OK