This project is heavily experimental and the implementation has missing parts. The source is extracted from a project and it was optimized for solving a simple pattern matching problem.

For a better and fully-functioning pattern matching in Typescript, please see ts-pattern library.

https://github.com/gvergnaud/ts-pattern

Pattern Matching in Typescript

Fast and efficient pattern matching in Typescript.

Usage

type Action = {
  target: string;
  event: "mousedown" | "mouseup" | "mousemove" | "touchmove";
  timestamp: number;
};
const uiAction = {target: "button-1", "event": "mousedown", "timestamp": 1} as Action;

pattern<Action>(uiAction)
  .case({target: "button-2", "event": "mousedown", timestamp: placeholder}, ({ timestamp }) => timestamp)
  .case({target: "button-1", "event": "mousedown", timestamp: placeholder}, ({ timestamp }) => timestamp)
  .case({target: "button-1", "event": "test", timestamp: placeholder}, ({ timestamp }) => timestamp)
  .case({target: "button-1", "event": "mousedown", timestamp: placeholder}, ({ timestamp }) => timestamp)
  .match() // 1

Fall-through

The second argument of case method is optional. In case if it's not given, the handler of next matched case statement will be evaluated.

type Action = {
  target: string;
  event: "mousedown" | "mouseup" | "mousemove" | "touchmove";
  timestamp: number;
};
const uiAction = {target: "button-1", "event": "mousedown", "timestamp": 1} as Action;

pattern<Action>(uiAction)
  .case({target: "button-2", "event": "mousedown", timestamp: placeholder})
  .case({target: "button-1", "event": "mousedown", timestamp: placeholder})
  .case({target: "button-1", "event": "test", timestamp: placeholder})
  .case({target: "button-1", "event": "mousedown", timestamp: placeholder}, ({ timestamp }) => timestamp)
  .match() // 1

Comparison with ts-pattern

console.time('ts-pattern')
const result = match<Action>(uiAction)
.with({target: "button-2", "event": "mousedown", timestamp: __}, ({ timestamp }) => timestamp)
.with({target: "button-1", "event": "mousedown", timestamp: __}, ({ timestamp }) => timestamp)
.with({target: "button-1", "event": "test", timestamp: __}, ({ timestamp }) => timestamp)
.with({target: "button-1", "event": "mousedown", timestamp: __}, ({ timestamp }) => timestamp)
.run();
console.log('result', result);
console.timeEnd('ts-pattern');

console.time('pattern-select')
const result2 = pattern<Action>(uiAction)
.case({target: "button-2", "event": "mousedown", timestamp: placeholder}, ({ timestamp }) => timestamp)
.case({target: "button-1", "event": "mousedown", timestamp: placeholder}, ({ timestamp }) => timestamp)
.case({target: "button-1", "event": "test", timestamp: placeholder}, ({ timestamp }) => timestamp)
.case({target: "button-1", "event": "mousedown", timestamp: placeholder}, ({ timestamp }) => timestamp)
.match()
console.log('result', result2);
console.timeEnd('pattern-select');

Blog post

https://fatih-erikli.com/pattern-matching-in-typescript.html

Happy hacking!