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Otherwise

Last Updated: 3/6/2026

.otherwise()

Runs the pattern-matching expression with a default handler which will be called if no previous .with() clause matches the input value, and returns the result.

Signature

function otherwise(defaultHandler: (value: TInput) => TOutput): TOutput;

Arguments

defaultHandler: (value: TInput) => TOutput

  • Required
  • Function called if no pattern matched the input value.
  • Think of it as the default: case of switch statements.
  • All handlers on a single match case must return values of the same type, TOutput.

Example

import { match, P } from 'ts-pattern';
 
const toString = (value: unknown): string =>
  match(value)
    .with(P.string, (str) => str)
    .with(P.number, (num) => num.toFixed(2))
    .with(P.boolean, (bool) => `${bool}`)
    .otherwise(() => 'Unknown');
 
console.log(toString('hello')); // 'hello'
console.log(toString(42)); // '42.00'
console.log(toString(true)); // 'true'
console.log(toString(null)); // 'Unknown'

Comparison with .exhaustive()

.otherwise() is useful when:

  • You don’t need exhaustiveness checking
  • You want to provide a catch-all case
  • Your input type is unknown or very broad

.exhaustive() is better when:

  • You want compile-time guarantees that all cases are handled
  • You’re working with discriminated unions
  • You want TypeScript to catch missing cases
// Using .otherwise() - no exhaustiveness checking
const handleStatus1 = (status: 'idle' | 'loading') =>
  match(status)
    .with('idle', () => 'Ready')
    .otherwise(() => 'Not ready'); // Catches 'loading'
 
// Using .exhaustive() - compile-time checking
const handleStatus2 = (status: 'idle' | 'loading') =>
  match(status)
    .with('idle', () => 'Ready')
    .with('loading', () => 'Loading...') // Must handle all cases
    .exhaustive();
OverviewReturnType