@onegen/optional

Optional utility class in TypeScript, based on C++ std::optional.

Made as minimally as I could, without any dependencies.
I just like how std::optional works and wanted it in JS/TS.
Guess it’s mostly done unless I find some mistake or something. 🤷🏼‍♂️

import { Optional } from "@onegen/optional";

function safeDiv (x: number, y: number): Optional<number> {
     if (y === 0) return Optional.nullopt;
     return Optional.some(x / y);
}

var result = safeDiv(2, 0);
if (!result.hasValue())
     console.log('Dividing be zero again, you dummy?');
else
     console.log('Result:', result.value());

Optional is a wrapper helper class around a value that may or may not be defined. Instead of returning some arbitrary value (like -1), null or throwing an error, Optional can be returned, prompting you – the dev – to first check if there is any value before actually using it in a fun and type safe manner! Look, it’s not for everyone, but I like it, OK?

Working with Optionals

Declaring

import { Optional, some } from '@onegen/optional';

var opt1 = new Optional<number>(2024);
var opt2 = Optional.some(2024);
var opt3 = some(2024)

All of these lines are equivalent. They create an Optional holding a number value 2024. First line specifies the type explicitly, second implies it from its value, third line is just a shorthand for the second.

As you – a smart TypeScript developer – might’ve guessed, you can’t change the Optional type. Once you make an instance of Optional<T>, the variable will only ever have Optional<T>.

var opt = Optional.some(2024);
opt = Optional.some('2024'); // TS won’t let you do this!

You can change the value, of course:

var opt = Optional.some(2024);
opt = Optional.some(2025);

// ..or as of 1.1.0 with a method:
opt.assign(2026);

…and even remove it:

var opt = Optional.some(2024);
opt = Optional.none();
opt = Optional.nullopt; // equivalent to Optional.none()

Do mind that this doesn’t clear the variable type. The variable is still Optional<number>, even if nullopt. It will ever contain only a number or nothing.

Typeless declaration

Be mindful when creating empty Optionals:

var opt = Optional.none()

The type of opt is Optional<unknown> and that is not something you really want now. I wish I could somehow forbid this, but oh well. Seriously, don’t do that. When making an empty Optional, specify its type explicitly, for your own sanity:

var opt: Optional<number> = Optional.none();
var opt = new Optional<number>();

Both these options work perfectly fine.

Base usage

The main advantage of Optional is that you don’t need an arbitrary "did not work" value (-1) or use nulls that you may forgot to check for. Optional makes it natural (at least for me) to check if it has a value before actually using it:

const result: Optional<number> = saferDivide(10, 0);
if (!result.hasValue())
     return "Whoops, something went wrong!"

const value = result.value();

Calling result.value() while there is no value will lead to an error.

If you want a more comprehensive Rust-like Result utility for error handling, you might want to take a look at neverthrow. It has a lot more functionality for error handling, Optional is just a simple "has value or has no value" wrapper. With a few more functions copied from C++:

Functions

Observers

Function	Return Type	Description
Optional.hasValue()	boolean	Checks whether the object contains a value
Optional.value()	T	Returns the included value (throws error if there is none)
Optional.valueOr(defaultValue: T)	T	Returns either the included value OR provided default value

Modifiers

Function	Return Type	Description
Optional.reset()	this	Removes the contained value
Optional.assign()	this	Assigns a new contained value
Optional.swap(other: Optional<T>)	this	Swaps values of same-type Optionals

C++ also has emplace(), but TS types cannot be used to make new instances, as far as I know.

assign() is also deviance from std::optional, but I chose to add it, as TS/JS does not allow operator overloading.

Also, all modifier methods return themselves (this) to allow chaining.

var opt = Optional.some(2024);
opt.reset().assign(2025).reset();

Monadic Operations

Function	Return Type	Description
Optional.andThen<U> (fn: (value: T) => Optional<U>)	Optional<U>	–
Optional.transform<U> (fn: (value: T) => U)	Optional<U>	–
Optional.orElse (fn: () => Optional<T>)	Optional<U>	–

These are harder to explain in short Markdown table, there are simple usage examples in optional-mon.test.ts. Who am I even writing this for nobody will use this except me lmao.

Licence

@onegen/optional is available as an open-source utility library licenced under the MIT Licence.

• TL;DR;NAL: Do absolutely whatever you want with the code, just include the LICENCE file if you re-distribute it.
• See LICENCE file or tl;drLegal for more details.