Utils
PromiseType
Extracts the resolved type of a Promise.
The PromiseType<T> utility type is designed to extract the inner resolved type from a Promise.
If the provided type T is a Promise, it will unwrap it and return the type it resolves to. If T is not a Promise, it simply returns T as-is.
Definition
PromiseType.ts
/**
* Extracts the resolved type of a Promise.
*/
export type PromiseType<T> = T extends Promise<infer U> ? U : T;
Example Usage
This utility is particularly helpful when you need to specifically type the return value of an asynchronous function without manually unwrapping the Promise using Awaited, or when dealing with higher-order functions that wrap existing asynchronous operations.
example.ts
import type { PromiseType } from '@riavzon/utils'
// A typical async function returning a string
async function fetchGreeting(): Promise<string> {
return "Hello, World!";
}
// Extracting the return type of the function
type AsyncGreetingReturn = ReturnType<typeof fetchGreeting>; // Promise<string>
// Unwrapping the Promise to get the actual resolved type
type Greeting = PromiseType<AsyncGreetingReturn>; // string
// Allowed
const message: Greeting = "Hello Nuxt!";
// Error: Type 'number' is not assignable to type 'string'.
const invalidMessage: Greeting = 123;
// If passed a non-Promise type, it returns the type as-is
type RegularString = PromiseType<string>; // string
