# Async Functions & Promise Types — TypeScript Fundamentals

Source: https://www.geekswithgeeks.com/en/typescript/ts-async-promises

> Type asynchronous code with Promise<T> and async/await, and handle errors safely under strict mode.

An `async` function always returns a `Promise`. Declare the resolved type inside `Promise<T>`.

```ts
interface User { id: number; name: string }

async function fetchUser(id: number): Promise<User> {
  const res = await fetch(`/api/users/${id}`);
  return (await res.json()) as User;
}

const user = await fetchUser(1); // user: User
```

`Promise.all` keeps a type per position, and `try/catch` errors are `unknown` under strict mode, so narrow them.

```ts
const [a, b] = await Promise.all([fetchUser(1), Promise.resolve("ok")]);
// a: User, b: string

try {
  await fetchUser(2);
} catch (e) {
  if (e instanceof Error) console.log(e.message);
}
```

Quick check

**Quiz:** What is the return type of `async function f(): Promise<number>`?

- [ ] number
- [x] Promise<number>
- [ ] void
- [ ] unknown

*Answer:* Promise<number>. An async function always wraps its result in a Promise.