Section 2: Lab: Type Safe Creators

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

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+# Lab: Type Safe Creators
+
+## Requirements
+
+1. There are eight pesky type errors in the Step 1 section of `start.ts`. Use the `satisfies` operator to help you fix them.
+2. In the `for...of` loop in Step 2 section, `Array.isArray` is used to narrow the type for the `creator` variable. Refactor this code to use type predicates to narrow the type instead.
+    1. Create two type predicate functions: `isDirector()` and `isProducer()`
+    2. Hint: The return type for these functions should be a type predicate where the type is an intersection type.

02-improving-type-safety/lab/solution.ts

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+interface Creator {
+  firstName: string;
+  lastName: string;
+  authored?: string[];
+  created?: string[];
+  directed?: string[];
+  produced?: string[];
+}
+
+// ---- STEP 1 ----
+
+console.log("\n>>>> STEP 1 <<<<\n");
+
+const authors = [
+  {
+    firstName: "Harper",
+    lastName: "Lee",
+    authored: ["To Kill a Mockingbird", "Go Set a Watchman"],
+  },
+  {
+    firstName: "Aldous",
+    lastName: "Huxley",
+    authored: ["Brave New World", "The Doors of Perception"],
+  },
+] satisfies Creator[];
+
+const artists = [
+  {
+    firstName: "Pink",
+    lastName: "Floyd",
+    created: ["The Dark Side of the Moon", "The Wall"],
+  },
+  {
+    firstName: "Snoop",
+    lastName: "Dogg",
+    created: ["Tha Doggfather", "Coolaid"],
+  },
+] satisfies Creator[];
+
+const directors = [
+  {
+    firstName: "Christopher",
+    lastName: "Nolan",
+    directed: ["Inception", "Interstellar"],
+  },
+  {
+    firstName: "Stanley",
+    lastName: "Kubrick",
+    directed: ["2001: A Space Odyssey", "A Clockwork Orange"],
+  },
+] satisfies Creator[];
+
+const producers = [
+  {
+    firstName: "Emma",
+    lastName: "Thomas",
+    produced: ["Inception", "Interstellar"],
+  },
+  {
+    firstName: "Katharina",
+    lastName: "Otto-Bernstein",
+    produced: ["Absolute Wilson", "Beuys"],
+  },
+] satisfies Creator[];
+
+const creators = {
+  authors,
+  artists,
+  directors,
+  producers,
+} satisfies Record<string, Creator[]>;
+
+for (let creator of creators.authors) {
+  console.log(
+    `${creator.firstName} ${
+      creator.lastName
+    } is an author who wrote the books ${creator.authored.join(", ")}`
+  );
+}
+
+for (let creator of creators.artists) {
+  console.log(
+    `${creator.firstName} ${
+      creator.lastName
+    } is an artist who created the albums ${creator.created.join(", ")}`
+  );
+}
+
+for (let creator of creators.directors) {
+  console.log(
+    `${creator.firstName} ${
+      creator.lastName
+    } is a director who directed the movies ${creator.directed.join(", ")}`
+  );
+}
+
+for (let creator of creators.producers) {
+  console.log(
+    `${creator.firstName} ${
+      creator.lastName
+    } is a producer who produced the movies ${creator.produced.join(", ")}`
+  );
+}
+
+// ---- STEP 2 ----
+
+console.log("\n>>>> STEP 2 <<<<\n");
+
+function isDirector(creator: Creator): creator is Creator & { directed: string[] } {
+  return creator.directed !== undefined;
+}
+
+function isProducer(creator: Creator): creator is Creator & { produced: string[] } {
+  return creator.produced !== undefined;
+}
+
+const filmCreators: Creator[] = [...directors, ...producers];
+
+for (let creator of filmCreators) {
+  let creatorType = "<unknown>";
+  let created: string[] = [];
+
+  if (isDirector(creator)) {
+    creatorType = "director";
+    created = creator.directed;
+  } else if (isProducer(creator)) {
+    creatorType = "producer";
+    created = creator.produced;
+  }
+
+  console.log(
+    `${creator.firstName} ${
+      creator.lastName
+    } is a ${creatorType} who helped create ${created.join(", ")}`
+  );
+}

02-improving-type-safety/lab/start.ts

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+interface Creator {
+  firstName: string;
+  lastName: string;
+  authored?: string[];
+  created?: string[];
+  directed?: string[];
+  produced?: string[];
+}
+
+// ---- STEP 1 ----
+
+console.log("\n>>>> STEP 1 <<<<\n");
+
+const authors: Creator[] = [
+  {
+    firstName: "Harper",
+    lastName: "Lee",
+    authored: ["To Kill a Mockingbird", "Go Set a Watchman"],
+  },
+  {
+    firstName: "Aldous",
+    lastName: "Huxley",
+    authored: ["Brave New World", "The Doors of Perception"],
+  },
+];
+
+const artists: Creator[] = [
+  {
+    firstName: "Pink",
+    lastName: "Floyd",
+    created: ["The Dark Side of the Moon", "The Wall"],
+  },
+  {
+    firstName: "Snoop",
+    lastName: "Dogg",
+    created: ["Tha Doggfather", "Coolaid"],
+  },
+];
+
+const directors: Creator[] = [
+  {
+    firstName: "Christopher",
+    lastName: "Nolan",
+    directed: ["Inception", "Interstellar"],
+  },
+  {
+    firstName: "Stanley",
+    lastName: "Kubrick",
+    directed: ["2001: A Space Odyssey", "A Clockwork Orange"],
+  },
+];
+
+const producers: Creator[] = [
+  {
+    firstName: "Emma",
+    lastName: "Thomas",
+    produced: ["Inception", "Interstellar"],
+  },
+  {
+    firstName: "Katharina",
+    lastName: "Otto-Bernstein",
+    produced: ["Absolute Wilson", "Beuys"],
+  },
+];
+
+const creators: Record<string, Creator[]> = {
+  authors,
+  artists,
+  directors,
+  producers,
+};
+
+for (let creator of creators.authors) {
+  console.log(
+    `${creator.firstName} ${
+      creator.lastName
+    } is an author who wrote the books ${creator.authored.join(", ")}`
+  );
+}
+
+for (let creator of creators.artists) {
+  console.log(
+    `${creator.firstName} ${
+      creator.lastName
+    } is an artist who created the albums ${creator.created.join(", ")}`
+  );
+}
+
+for (let creator of creators.directors) {
+  console.log(
+    `${creator.firstName} ${
+      creator.lastName
+    } is a director who directed the movies ${creator.directed.join(", ")}`
+  );
+}
+
+for (let creator of creators.producers) {
+  console.log(
+    `${creator.firstName} ${
+      creator.lastName
+    } is a producer who produced the movies ${creator.produced.join(", ")}`
+  );
+}
+
+// ---- STEP 2 ----
+
+console.log("\n>>>> STEP 2 <<<<\n");
+
+const filmCreators: Creator[] = [...directors, ...producers];
+
+for (let creator of filmCreators) {
+  let creatorType = "<unknown>";
+  let created: string[] = [];
+
+  if (Array.isArray(creator.directed)) {
+    creatorType = "director";
+    created = creator.directed;
+  } else if (Array.isArray(creator.produced)) {
+    creatorType = "producer";
+    created = creator.produced;
+  }
+
+  console.log(
+    `${creator.firstName} ${
+      creator.lastName
+    } is a ${creatorType} who helped create ${created.join(", ")}`
+  );
+}

02-improving-type-safety/lab/tsconfig.json

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