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Option, Result, and Either types for JavaScript

🦀 Inspired by Rust

Zero dependencies • Lightweight • Functional

Install

npm install @thames/monads

Getting started

The Option<T> type

Option represents an optional value: every Option is either Some and contains a value, or None, and does not.

[!NOTE]

Full documentation here: Option

import { Option, Some, None } from '@thames/monads';
const divide = (numerator: number, denominator: number): Option<number> => {   if (denominator === 0) {     return None;   } else {     return Some(numerator / denominator);   } };
// The return value of the function is an option const result = divide(2.0, 3.0);
// Pattern match to retrieve the value const message = result.match({   some: (res) => Result: ${res},   none: 'Cannot divide by 0', });
console.log(message); // "Result: 0.6666666666666666"

The Result<T, E> type

Result represents a value that is either a success (Ok) or a failure (Err).

[!NOTE]

Full documentation here: Result

import { Result, Ok, Err } from '@thames/monads';
const getIndex = (values: string[], value: string): Result<number, string> => {   const index = values.indexOf(value);
switch (index) {     case -1:       return Err('Value not found');     default:       return Ok(index);   } };
const values = ['a', 'b', 'c'];
getIndex(values, 'b'); // Ok(1) getIndex(values, 'z'); // Err("Value not found")

The Either<L, R> type

Either represents a value that is either Left or Right. It is a powerful way to handle operations that can result in two distinctly different types of outcomes.

[!NOTE]

Full documentation here: Either

import { Either, Left, Right } from '@thames/monads';
const divide = (numerator: number, denominator: number): Either<string, number> => {   if (denominator === 0) {     return Left('Cannot divide by 0');   } else {     return Right(numerator / denominator);   } };
const result = divide(2.0, 3.0);
const message = result.match({   left: (err) => Error: ${err},   right: (res) => Result: ${res}, });
console.log(message); // "Result: 0.6666666666666666"