@philiprehberger/match-ts

Pattern matching for TypeScript -- switch on steroids

Installation

npm install @philiprehberger/match-ts

Usage

import { match, P } from "@philiprehberger/match-ts";

// Literal matching
const label = match(statusCode)
  .with(200, () => "OK")
  .with(404, () => "Not Found")
  .with(500, () => "Server Error")
  .otherwise(() => "Unknown");

// Type matchers
const type = match(value)
  .with(P.string, () => "string")
  .with(P.number, () => "number")
  .with(P.boolean, () => "boolean")
  .otherwise(() => "other");

// Object shape matching
const message = match(event)
  .with({ type: "login", user: P.select("name") }, (_v, sel) => `Welcome ${sel.name}`)
  .with({ type: "logout" }, () => "Goodbye")
  .exhaustive();

// Guard predicates
const size = match(count)
  .with(P.when((n) => n > 100), () => "large")
  .with(P.when((n) => n > 10), () => "medium")
  .otherwise(() => "small");

// Union matching
const color = match(input)
  .with(P.union("red", "green", "blue"), () => "primary")
  .otherwise(() => "other");

// Array matching
const result = match(data)
  .with(P.array(P.number), (nums) => nums.reduce((a, b) => a + b, 0))
  .otherwise(() => 0);

// Exhaustive matching (throws if no pattern matches)
const output = match(action)
  .with("start", () => startProcess())
  .with("stop", () => stopProcess())
  .exhaustive();

API

| Export | Description | | --- | --- | | match(value) | Start a match expression, returns a chainable builder | | .with(pattern, handler) | Add a match case; handler receives (value, selections) | | .otherwise(handler) | Default case; always matches, returns handler result | | .exhaustive() | Finalize; throws if no pattern matched | | .run() | Alias for .exhaustive() | | P.string | Matches any string | | P.number | Matches any number | | P.boolean | Matches any boolean | | P.nullish | Matches null or undefined | | P.any | Matches any value | | P.when(fn) | Matches when fn(value) returns true | | P.union(...values) | Matches if any value/pattern in the union matches | | P.instanceOf(Class) | Matches instances of the given class | | P.select(name?) | Captures the matched value into selections | | P.array(pattern) | Matches arrays where every element matches the pattern |

Development

npm install
npm run build
npm test

License

MIT