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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> = ( { status: 'success'; data: T; } | { status: 'error'; error: string; } );
export function promisify<T>(arg: (callback: (response: ApiResponse<T>) => void) => void): () => Promise<T> { return () => new Promise<T>((resolve, reject) => arg(response => response.status === 'success'? resolve(response.data) : reject(response.error))); }
const oldApi = { requestAdmins(callback: (response: ApiResponse<Admin[]>) => void) { callback({ status: 'success', data: admins }); }, requestUsers(callback: (response: ApiResponse<User[]>) => void) { callback({ status: 'success', data: users }); }, requestCurrentServerTime(callback: (response: ApiResponse<number>) => void) { callback({ status: 'success', data: Date.now() }); }, requestCoffeeMachineQueueLength(callback: (response: ApiResponse<number>) => void) { callback({ status: 'error', error: 'Numeric value has exceeded Number.MAX_SAFE_INTEGER.' }); } };
export const api = { requestAdmins: promisify(oldApi.requestAdmins), requestUsers: promisify(oldApi.requestUsers), requestCurrentServerTime: promisify(oldApi.requestCurrentServerTime), requestCoffeeMachineQueueLength: promisify(oldApi.requestCoffeeMachineQueueLength) };
function logPerson(person: Person) { console.log( ` - ${person.name}, ${person.age}, ${person.type === 'admin' ? person.role : person.occupation}` ); }
async function startTheApp() { console.log('Admins:'); (await api.requestAdmins()).forEach(logPerson); console.log();
console.log('Users:'); (await api.requestUsers()).forEach(logPerson); console.log();
console.log('Server time:'); console.log(` ${new Date(await api.requestCurrentServerTime()).toLocaleString()}`); console.log();
console.log('Coffee machine queue length:'); console.log(` ${await api.requestCoffeeMachineQueueLength()}`); }
startTheApp().then( () => { console.log('Success!'); }, (e: Error) => { console.log(`Error: "${e.message}", but it's fine, sometimes errors are inevitable.`); } );
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