ts-opt

Typed Option/Maybe for TypeScript and JavaScript (based on Scala, Haskell and Sanctuary), created to simplify code involving optional values.

Features

• ⛓️ TypeScript Support
  • ⚙️ Strict types - it's a TypeScript-first library, no wild anys
  • but it is fully usable from JavaScript as well
• 🔩 Pragmatic - doesn't force functional programming paradigm
• 📏 100% Test Coverage
• 🗜️ Lightweight - no dependencies, only around 3KiB gzip+minified

Installation

npm i -S ts-opt

Examples

In all examples opt import is presumed to be present:

import { opt } from 'ts-opt';

Basic use

    // without
    const f = (name: string | undefined) => {
      if (!name || name === '') { throw new Error('Missing name.'); }
      return name[0];
    };

    // with
    const g = (name: string | undefined) => opt(name).orCrash('Missing name.')[0];

    f('Riker'); // 'R'
    g('Riker'); // 'R'

    f(undefined); // exception thrown
    g(undefined); // exception thrown

caseOf

    const fireMissiles = () => { console.log('FIRING!'); };
    const printSuccess = (x: string) => { console.log(x); };

    const handleMoveVanilla = (usersMove?: string): void => usersMove ? printSuccess(usersMove) : fireMissiles();
    const handleMove = (usersMove?: string): void => opt(usersMove).caseOf(printSuccess, fireMissiles);

    handleMoveVanilla(); // prints FIRING!
    handleMove(); // prints FIRING!
    handleMoveVanilla('Build a pylon.'); // prints Build a pylon.
    handleMove('Build a pylon.'); // prints Build a pylon.

More advanced

interface Person {
  name: string;
  surname: string | null;
}

type Db = { [_: string]: Person };

/* ... */

    const db: Db = {
      '0': {name: 'John', surname: null},
      '1': {name: 'Worf', surname: 'Mercer'}
    };

    // without
    const f = (id: number | undefined): string | null => {
      if (id === undefined) { return null; }
      const item = db[id];
      if (!item) { return null; }
      const surname = item.surname ? item.surname.toUpperCase() : '<missing>';
      return item.name + ' ' + surname;
    };

    // with
    const g = (id: number | undefined): string | null => opt(id)
      .chainToOpt(x => db[x])
      .map(item => item.name + ' ' + opt(item.surname).map(x => x.toUpperCase()).orElse('<missing>'))
      .orNull();

    f(0); // 'John <missing>'
    g(0); // 'John <missing>'

    f(1); // 'Worf MERCER'
    g(1); // 'Worf MERCER'
    
    f(2); // null
    g(2); // null

Documentation

All methods are documented, if you don't see a description please make sure you are reading the base class page - Opt.

• Main Opt class
• Module (constructors and helper functions)

License

MIT