Section 2: Exercise: Library for a Library

02-improving-type-safety/exercise/README.md

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+# Exercise: Library for a Library
+
+In this exercise, we'll be creating a library with the following functions:
+
+- `describeItem(item: LibraryItem): void`
+- `getMovieById(id: Movie['id']): Promise<string>`

02-improving-type-safety/exercise/completed/data.ts

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+import { type Brand } from './utils.js';
+
+export interface Book {
+  type: 'book',
+  id: string;
+  title: string;
+  published: number;
+  author: string;
+}
+
+export interface Album {
+  type: 'album',
+  id: string;
+  title: string;
+  released: number;
+  artist: string;
+}
+
+export interface MotionPicture {
+  id: unknown;
+  title: string;
+  released: number;
+  director: string;
+}
+
+export interface Movie extends MotionPicture {
+  type: 'movie',
+  id: Brand<string, 'MovieId'>;
+}
+
+export interface Show extends MotionPicture {
+  type: 'show',
+  id: Brand<string, 'ShowId'>;
+}
+
+export type LibraryItem = Book | Album | Movie | Show;
+
+export const book: Book = {
+  type: 'book',
+  id: '82f7c297-40ec-4e9f-90b0-a12f2b4980c1',
+  title: 'To Kill a Mockingbird',
+  published: 1960,
+  author: 'Harper Lee'
+}
+
+export const album: Album = {
+  type: 'album',
+  id: '1dc8dd44-245e-4a5f-b1b6-8c02fd2a9dc1',
+  title: 'The Dark Side of the Moon',
+  released: 1973,
+  artist: 'Pink Floyd'
+};
+
+export const movie: Movie = {
+  type: 'movie',
+  id: 'f928756a-d3d9-4db3-92ea-88100d03af47' as Movie['id'],
+  title: 'Point Break',
+  released: 1991,
+  director: 'Kathryn Bigelow'
+};
+
+export const show: Show = {
+  type: 'show',
+  id: 'c9a7b229-b48f-4407-a267-45ff7fe8ea60' as Show['id'],
+  title: 'Westworld',
+  released: 2016,
+  director: 'Jonathan Nolan'
+};

02-improving-type-safety/exercise/completed/index.ts

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+import {
+  book,
+  album,
+  movie,
+  show,
+  type Book,
+  type Album,
+  type Movie,
+  type Show,
+  type LibraryItem,
+} from "./data.js";
+
+import { fetchApiData } from "./utils.js";
+
+function isBook(item: LibraryItem): item is Book {
+  return item.type === "book";
+}
+
+function isAlbum(item: LibraryItem): item is Album {
+  return item.type === "album";
+}
+
+function isMovie(item: LibraryItem): item is Movie {
+  return item.type === "movie";
+}
+
+function isShow(item: LibraryItem): item is Show {
+  return item.type === "show";
+}
+
+function describeLibraryItem(item: LibraryItem) {
+  if (isBook(item)) {
+    console.log(
+      `- ${item.title} is a book written by ${item.author}, and published in ${item.published}.`
+    );
+  } else if (isAlbum(item)) {
+    console.log(
+      `- ${item.title} is an album by the artist ${item.artist}, released in ${item.released}`
+    );
+  } else if (isMovie(item)) {
+    console.log(
+      `- ${item.title} is a movie directed by ${item.director}, released in ${item.released}`
+    );
+  } else if (isShow(item)) {
+    console.log(
+      `- ${item.title} is a show directed by ${item.director}, released in ${item.released}`
+    );
+  } else {
+    console.error("Error: Unrecognised library item!");
+  }
+}
+
+describeLibraryItem(book);
+describeLibraryItem(album);
+describeLibraryItem(movie);
+describeLibraryItem(show);
+
+function assertIsMovie(item: LibraryItem): asserts item is Movie {
+  if (item.type !== 'movie') {
+    throw new Error(`This item is not a Movie: ${item.title}`);
+  }
+}
+
+async function getMovieById(id: Movie['id']) {
+  const apiData = await fetchApiData();
+
+  const movie = apiData.find((item: LibraryItem) => item.id === id);
+
+  if (!movie) {
+    throw new Error('Movie not found');
+  }
+
+  assertIsMovie(movie);
+
+  return movie;
+}
+
+const movieDetails = await getMovieById(movie.id);
+
+console.log(movieDetails);

02-improving-type-safety/exercise/completed/tsconfig.json

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+{
+  "extends": "@total-typescript/tsconfig/tsc/no-dom/app"
+}

02-improving-type-safety/exercise/completed/utils.ts

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+import { movie, show, book, album } from "./data.js";
+
+export async function fetchApiData() {
+  const data = [movie, show, book, album];
+  const apiResponse = structuredClone(data);
+  return apiResponse;
+}
+
+declare const __brand: unique symbol;
+
+export type Brand<BaseType, BrandedName extends string> = BaseType & {
+  [__brand]: BrandedName;
+};

02-improving-type-safety/exercise/start/data.ts

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+export const book = {
+  type: 'book',
+  id: '82f7c297-40ec-4e9f-90b0-a12f2b4980c1',
+  title: 'To Kill a Mockingbird',
+  published: 1960,
+  author: 'Harper Lee'
+}
+
+export const album = {
+  type: 'album',
+  id: '1dc8dd44-245e-4a5f-b1b6-8c02fd2a9dc1',
+  title: 'The Dark Side of the Moon',
+  released: 1973,
+  artist: 'Pink Floyd'
+};
+
+export const movie = {
+  type: 'movie',
+  id: 'f928756a-d3d9-4db3-92ea-88100d03af47',
+  title: 'Point Break',
+  released: 1991,
+  director: 'Kathryn Bigelow'
+};
+
+export const show = {
+  type: 'show',
+  id: 'c9a7b229-b48f-4407-a267-45ff7fe8ea60',
+  title: 'Westworld',
+  released: 2016,
+  director: 'Jonathan Nolan'
+};

02-improving-type-safety/exercise/start/index.ts

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+import { book, album, movie, show } from "./data.js";
+
+import { fetchApiData } from "./utils.js";

02-improving-type-safety/exercise/start/tsconfig.json

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+{
+  "extends": "@total-typescript/tsconfig/tsc/no-dom/app"
+}

02-improving-type-safety/exercise/start/utils.ts

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+import { movie, show, book, album } from "./data.js";
+
+export async function fetchApiData() {
+  const data = [movie, show, book, album];
+  const apiResponse = structuredClone(data);
+  return apiResponse;
+}
+
+declare const __brand: unique symbol;
+
+export type Brand<BaseType, BrandedName extends string> = BaseType & {
+  [__brand]: BrandedName;
+};