generics

src/07-funktionsprogrammierung/generics.ts

@@ -0,0 +1,91 @@
+function getFirstElement(arr: any[]): any {
+  return arr[0];
+}
+
+const first = getFirstElement(['Hello', 'World']);
+console.log(first.toUpperCase());
+
+function getFirstElementGeneric<T>(arr: T[]): T {
+  return arr[0];
+}
+const array = ['Hello', '1', 'World'];
+const firstGen = getFirstElementGeneric<string>(array);
+console.log(firstGen.length);
+
+class UserRepository {
+  private users: string[] = [];
+
+  add(user: string) {
+    this.users.push(user);
+  }
+
+  getAll(): string[] {
+    return this.users;
+  }
+}
+
+class Repository<T> {
+  private items: T[] = [];
+
+  add(item: T) {
+    this.items.push(item);
+  }
+
+  getAll(): T[] {
+    return this.items;
+  }
+}
+
+const userRepo = new Repository<{ name: string; age: number }>();
+userRepo.add({ name: 'Alice', age: 28 });
+userRepo.add({ name: 'Bob', age: 42 });
+
+console.log(userRepo.getAll());
+
+async function fetchData<T>(url: string): Promise<T> {
+  const response = await fetch(url);
+  return response.json();
+}
+
+type User = {
+  id: number;
+  name: string;
+};
+
+export async function getUsers() {
+  const user = await fetchData<User>(
+    'https://jsonplaceholder.typicode.com/posts/1'
+    // 'https://jsonplaceholder.typicode.com/users/1'
+    // 'https://jsonplaceholder.typicode.com/users/1'
+  );
+  console.log(user.name);
+}
+
+// getUsers();
+
+function logLength<TKey extends { length: number }, TValue>(
+  item: TKey,
+  num?: TValue
+): void {
+  console.log(item.length);
+}
+
+logLength<string, number>('Hallo', 42);
+logLength(['a', 'b']);
+logLength(42);
+
+const obj = {
+  name: 'Alice',
+  age: 22,
+};
+
+console.log(Object.keys(obj));
+console.log(Object.getOwnPropertyNames(obj));
+
+function identity<T>(value: T): T {
+  return value;
+}
+
+function identity(value) {
+  return value;
+}