opt

Option types for TypeScript with real gradual typing.

API Docs

Find the API docs here:

• github.bodil.lol/opt

Rationale

There are several million implementations of option types on NPM. Many of them are implemented in plain JavaScript with no types. Nearly all of the remainder don't have very good type inference: their isSome() function just returns a boolean rather than a useful is assertion, or they exclusively use some other mechanism, like callbacks, to decide the type of the wrapped value. The very few cases remaining implement the option type as a simple object manipulated by external functions, rather than an object with attached methods, making them a little too cumbersome to work with.

This package gives you both, as well as a complete and fully documented API inspired by Rust's Option and Result types.

Example

Result in Node:

import { Ok, Result } from "@bodil/opt";

const result: Result<Date, Error> = Ok(new Date());

// result.value is Date | Error here.

if (result.isOk()) {
    // the type checker now knows that result.value must be a Date.
    console.log("Date:", result.value.toLocaleString());
} else {
    // the type checker knows result.value must be an Error in the else branch.
    console.log("Error:", result.value.message);
}

Option in Deno:

import { Option, Some } from "https://deno.land/x/opt/option.ts";

const option: Option<Date> = Some(new Date());

// option.value is Date | undefined here.

if (option.isSome()) {
    // the type checker now knows option.value is definitely a Date.
    console.log("Date:", option.value.toLocaleString());
} else {
    console.log("No value!");
}

Licence

Copyright 2023 Bodil Stokke

This software is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.