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interface User { type: 'user'; name: string; age: number; occupation: string; }
interface Admin { type: 'admin'; name: string; age: number; role: string; }
type Person = User | Admin;
const admins: Admin[] = [ { type: 'admin', name: 'Jane Doe', age: 32, role: 'Administrator' }, { type: 'admin', name: 'Bruce Willis', age: 64, role: 'World saver' } ];
const users: User[] = [ { type: 'user', name: 'Max Mustermann', age: 25, occupation: 'Chimney sweep' }, { type: 'user', name: 'Kate Müller', age: 23, occupation: 'Astronaut' } ];
export type ApiResponse<T> = unknown;
type AdminsApiResponse = ( { status: 'success'; data: Admin[]; } | { status: 'error'; error: string; } );
export function requestAdmins(callback: (response: AdminsApiResponse) => void) { callback({ status: 'success', data: admins }); }
type UsersApiResponse = ( { status: 'success'; data: User[]; } | { status: 'error'; error: string; } );
export function requestUsers(callback: (response: UsersApiResponse) => void) { callback({ status: 'success', data: users }); }
export function requestCurrentServerTime(callback: (response: unknown) => void) { callback({ status: 'success', data: Date.now() }); }
export function requestCoffeeMachineQueueLength(callback: (response: unknown) => void) { callback({ status: 'error', error: 'Numeric value has exceeded Number.MAX_SAFE_INTEGER.' }); }
function logPerson(person: Person) { console.log( ` - ${person.name}, ${person.age}, ${person.type === 'admin' ? person.role : person.occupation}` ); }
function startTheApp(callback: (error: Error | null) => void) { requestAdmins((adminsResponse) => { console.log('Admins:'); if (adminsResponse.status === 'success') { adminsResponse.data.forEach(logPerson); } else { return callback(new Error(adminsResponse.error)); }
console.log();
requestUsers((usersResponse) => { console.log('Users:'); if (usersResponse.status === 'success') { usersResponse.data.forEach(logPerson); } else { return callback(new Error(usersResponse.error)); }
console.log();
requestCurrentServerTime((serverTimeResponse) => { console.log('Server time:'); if (serverTimeResponse.status === 'success') { console.log(` ${new Date(serverTimeResponse.data).toLocaleString()}`); } else { return callback(new Error(serverTimeResponse.error)); }
console.log();
requestCoffeeMachineQueueLength((coffeeMachineQueueLengthResponse) => { console.log('Coffee machine queue length:'); if (coffeeMachineQueueLengthResponse.status === 'success') { console.log(` ${coffeeMachineQueueLengthResponse.data}`); } else { return callback(new Error(coffeeMachineQueueLengthResponse.error)); }
callback(null); }); }); }); }); }
startTheApp((e: Error | null) => { console.log(); if (e) { console.log(`Error: "${e.message}", but it's fine, sometimes errors are inevitable.`) } else { console.log('Success!'); } });
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