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πŸ‘» Type safe Option and Result type – for TypeScript and JavaScript
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slavovojacek fix(Option): [#70] Allow null in the constructor (#72)
* fix(Option): Allow null in the constructor

* 3.0.0

* fix(Package): Up version, fix author
Latest commit b004b2d Nov 7, 2019

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Type safe Option and Result types – inspired by Rust.

Prereqs & Install

  • Node >=9.10.0
  • npm >=6.1.0

Please note that the TypeScript target is ES6.

npm install @usefultools/monads




See full Option<T> API documentation here.

import { Option, Some, None } from "@usefultools/monads"

function 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"

More Option<T> examples here.

Result<T, E>

See full Result<T, E> API documentation here.

import { Result, Ok, Err } from "@usefultools/monads"

function getIndex(values: string[], value: string): Result<number, string> {
  const index = values.indexOf(value)

  switch (index) {
    case -1:
      return Err("Value not found")
    return Ok(index)

console.log(getIndex(["a", "b", "c"], "b")) // Ok(1)
console.log(getIndex(["a", "b", "c"], "z")) // Err("Value not found")

More Result<T, E> examples here.


If you have comments, complaints, or ideas for improvements, feel free to open an issue or a pull request! See Contributing guide for details about project setup, testing, etc.

Author and license

This library was created by Main author and maintainer is Slavo Vojacek.

Contributors: Slavo Vojacek

@usefultools/monads is available under the ISC license. See the LICENSE file for more info.

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