option.ts

Option monad for TypeScript.

Table of Contents

• Install
• Usage
• Type safety
• Contributing
• License

Install

$ npm install --save @kevinpollet/option.ts

Usage

import { from } from "@kevinpollet/option.ts";

const user: User | undefined = findById(42);

const name: string = from(user)
  .map(value => value.getName())
  .getOrElse("No Name");

💡 You may have noticed that Option monad does not play well with ES6 Promise. The following example shows that you need to write a lot of boilerplate code.

import { from } from "@kevinpollet/option.ts";

const user: Promise<Option<User>> = findById(42);

const name: Promise<Option<string>> = from(user).then(promiseValue =>
  promiseValue.map(value => value.getName())
);

To reduce this boilerplate option.ts adds support for asynchronous Option:

import { fromPromise } from "@kevinpollet/option.ts";

const user: Promise<Option<User>> = findById(42);

const name: PromiseOption<string> = fromPromise(user).map(value =>
  value.getName()
);

Type safety

You're strongly encouraged to add the strictNullChecks flag to your TypeScript compiler options. From TypeScript documentation:

In strict null checking mode, the null and undefined values are not in the domain of every type and are only assignable to themselves and any (the one exception being that undefined is also assignable to void).

With this flag the following code will not compile. Without strictNullChecks a TypeError will be thrown at runtime:

Some(null); // Compilation error
Some(undefined); // Compilation error

Contributing

Contributions are welcome!

Want to file a bug, request a feature or contribute some code?

1. Check out the Code of Conduct.
2. Check for an existing issue corresponding to your bug or feature request.
3. Open an issue to describe your bug or feature request.

License

MIT