sdedovic/option-ts

Option Monad for TypeScript

Option monad for Typescript

Yet another port of the Scala Option type to TypeScript.

npm i --save option-monad-ts

Usage

Basic Example

import { Option, Some, None } from 'option-monad-ts';

// Create Some 
let n = new Some(3);
let m = Some.of('four');

// Create Option
let c = Option.of(3);
let d = Option.of(null);

// Validate and use
n.get();                    // 3
m.get();                    // 'four'

c.isDefined();              // true
d.isDefined();              // false

Some.of(4)
    .map(_ => _.toString())
    .forEach(_ => console.log(_))

Documentation

Option<T>

static of<T>(x: T): Option<T>

An Option factory which creates Some.of(x) if the argument is not null, and None if it is null.

filter(p: (i: T) => boolean): Option<T>

Returns this Option if it is nonempty and applying the predicate p to this Option's value returns true. Otherwise, return None.

flatMap<R>(f: (i: T) => Option<R>): Option<R>

Returns the result of applying f to this Option's value if this Option is nonempty. Returns None if this Option is empty. Slightly different from map in that f is expected to return an Option (which could be None).

forEach<U>(f: (i: T) => U): void

Apply the given procedure f to the option's value, if it is nonempty. Otherwise, do nothing.

get(): T

Returns the option's value. The option must be nonEmpty.

getOrElse(defaultValue: T): T

Returns the option's value if the option is nonempty, otherwise return defaultValue.

isDefined(): boolean

Returns true if the option is an instance of Some, false otherwise.

isEmpty(): boolean

Returns true if the option is None, false otherwise.

map<R>(f: (i: T) => R): Option<R>

Returns a Some containing the result of applying f to this Option's value if this Option is nonempty. Otherwise, return None.

Why another library?

• I thought it would be a good exercise
• I didn't like the API/usage patterns of some existing libraries
• I wanted something as close to the Scala lib as possible, so I ported it trying to keep to its spirit