hiroshi-manabe / typescript-optional

Optional (like Java) implementation in TypeScript

TypeScript Optional

Optional (like Java) implementation in TypeScript

Overview

Optional<T> is a type which may contain a payload of type T or may not contain. It provides the common interface regardless of an instance is present or is empty.

This module reffers to Optional class in Java 8.

Install

npm install --save typescript-optional

Usage

import

// import Optional type from this module
import Optional from 'typescript-optional';

creating Optional<T> objects

let nullableString: string | null = /* some nullable value */;

// all the following variables will be parameterized as Optional<string>.
let optional = Optional.ofNullable(nullableString);
let optionalPresent1 = Optional.ofNullable("foo");
let optionalPresent2 = Optional.ofNonNull("foo"); // accepts non-null value (or else throws TypeError)
let optionalEmpty1: Optional<string> = Optional.empty(); // type hinting required
let optionalEmpty2 = Optional.empty<string>(); // or parameterize explicitly

operations

let optional: Optional<string> = Optional.ofNullable( /* some optional value */ );

// force to retrieve the payload. (or else throws TypeError.)
// this method is not used match.
optional.get();

// be whether a payload is present or not.
optional.isPresent

// be whether this is empty or not. (negation of `isPresent` property)
optional.isEmpty

// if a payload is present, execute the given procedure.
optional.ifPresent(value => console.log(value));

// filter a payload with additional predicate.
optional.filter(value => value.length > 0);

// map a payload with the given mapper.
optional.map(value => value.length);

// map a payload with the given mapper which returns value wrapped with Optional type.
let powerIfPositive: (x: Number) => Optional<Number>
    = x => (x > 0) ? Optional.ofNonNull(x * x) : Optional.empty();

optional.flatMap(value => powerIfPositive(value));

// retrieve a payload if this is present, return the given value or else.
optional.orElse("bar");

// retrieve a payload if this is present, return a value supplied by the given function or else.
optional.orElseGet(() => "bar");

// retrieve a payload if this is present, throws an exception supplied by the given function or else.
optional.orElseThrow(() => new Error());

License

MIT License - LICENSE.md