Option

type Option<T> = None | Some<T>;

An implementation of the Rust Option<T> type in JavaScript.

In Rust, optional values are represented using Option<T>, which can be either:

• Some(T), indicating a present value.
• None, indicating the absence of a value.

In JavaScript, this is typically represented as T | null. However, this approach fails with nested options. For example, Option<Option<T>> in Rust would translate to T | null | null in JavaScript, which is equivalent to T | null. This means there is no way to differentiate between Some(None) and None, making nested options impossible.

This Option type helps solve this by mirroring Rust’s Option<T> type.

type Option<T> = Some<T> | None;
type Some<T> = { __option: 'Some'; value: T };
type None = { __option: 'None' };

Type Parameters

Example

Here's how you can create Option values.

To improve developer experience, helper functions are available. TypeScript can infer the type of T or it can be explicitly provided.

// Create an option with a value.
some('Hello World');
some<number | string>(123);
 
// Create an empty option.
none();
none<number | string>();

See

• Some
• None
• some
• none