isErr - API reference

API reference › @evolu/common › Result › isErr

function isErr<T, E>(result: Result<T, E>): result is Err<E>;

Defined in: packages/common/src/Result.ts:408

Type guard for Err results.

Example

import {
  assertErr,
  assertType,
  err,
  isErr,
  type Err,
  type Result,
  type Typed,
} from "@evolu/common";

const getCount = (): Result<number, CountUnavailableError> =>
  err({ type: "CountUnavailable" });

interface CountUnavailableError extends Typed<"CountUnavailable"> {}

const count = getCount();
if (isErr(count)) {
  assertType<Err<CountUnavailableError>, typeof count>();
  assertErr(count, { type: "CountUnavailable" });
}