6.10: extending interfaces.

app/app.ts

@@ -1,4 +1,4 @@
-import {Book, DamageLogger} from './interfaces';
+import {Author, Book, DamageLogger, Librarian} from './interfaces';
 import {Category} from "./enums";
 
 function GetAllBooks(): Book[] {
@@ -156,5 +156,17 @@ let myBook: Book = {
 // PrintBook(myBook);
 // myBook.markDamaged('Torn back cover');
 
-let logDamage: DamageLogger = reason => console.log(`Damage reported: ${reason}.`);
-logDamage('Coffee stains');
+// let logDamage: DamageLogger = reason => console.log(`Damage reported: ${reason}.`);
+// logDamage('Coffee stains');
+
+let favoriteAuthor: Author = {
+  email: 'foo@example.com',
+  numBooksPublished: 1,
+  name: 'Foo',
+};
+let favoriteLibrarian: Librarian = {
+  email: "jane@example.com",
+  name: 'Jane Doe',
+  departement: 'Sales',
+  assistCustomer: (custName: string) => console.log(`Helping ${custName}.'), 
+}

app/interfaces.ts

@@ -15,7 +15,23 @@ interface Book {
   markDamaged?: DamageLogger,
 }
 
+interface Person {
+  name: string;
+  email: string;
+}
+
+interface Author extends Person {
+  numBooksPublished: number;
+}
+
+interface Librarian extends Person {
+  departement: string;
+  assistCustomer: (custName: string) => void,
+}
+
 export {
+  Author,
   Book,
   DamageLogger,
+  Librarian,
 }