Overview
The errAsync function constructs a ResultAsync containing an Err variant with the provided error value.
Signature
function errAsync<T = never, E extends string = string>(err: E): ResultAsync<T, E>
function errAsync<T = never, E = unknown>(err: E): ResultAsync<T, E>
function errAsync<T = never, E extends void = void>(err: void): ResultAsync<T, void>
The error value to wrap in a ResultAsync
ResultAsync<T, E> - A ResultAsync containing the Err value
Usage
Basic usage
import { errAsync } from 'neverthrow'
const myResultAsync = errAsync('Oh nooo')
const myResult = await myResultAsync
myResult.isOk() // false
myResult.isErr() // true
Async error handling
async function validateAge(age: number) {
if (age < 0) {
return errAsync('Age cannot be negative')
}
if (age < 18) {
return errAsync('Must be 18 or older')
}
return okAsync(age)
}
const result = await validateAge(15)
// Result<number, string>
Custom error types
type DatabaseError =
| { type: 'ConnectionError', message: string }
| { type: 'QueryError', query: string }
async function queryDatabase(sql: string) {
return errAsync<User[], DatabaseError>({
type: 'QueryError',
query: sql
})
}
When to use
- Returning an error from an async operation
- Early returns in validation chains
- Converting error states to ResultAsync for consistency
Like okAsync, this wraps the error in a resolved Promise. The Promise itself does not reject.
okAsync
Create an Ok variant of ResultAsync
ResultAsync.fromPromise
Handle rejecting Promises