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Last Updated: 3/6/2026

Patterns

A pattern is a description of the expected shape of your input value.

Patterns can be regular JavaScript values ("some string", 10, true, …), data structures (objects, arrays, …), wildcards (P._, P.string, P.number, …), or special matcher functions (P.not, P.when, P.select, …).

All wildcards and matcher functions can be imported either as Pattern or as P from the ts-pattern module.

import { match, Pattern } from 'ts-pattern';
 
const toString = (value: unknown): string =>
  match(value)
    .with(Pattern.string, (str) => str)
    .with(Pattern.number, (num) => num.toFixed(2))
    .with(Pattern.boolean, (bool) => `${bool}`)
    .otherwise(() => 'Unknown');

Or:

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');

Pattern Types

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