Option

Safe handling of nullable values.

Overview

Option is a container that either holds a value (Some) or represents the absence of a value (None). It eliminates null pointer exceptions by making nullable values explicit in the type system.

Basic Usage

import { Option } from "functype/option"

// Creating Options
const some = Option(42) // Some(42)
const none = Option(null) // None
const explicit = Option.none() // None

// Checking state
some.isSome() // true
none.isNone() // true

// Extracting values
some.orElse(0) // 42
none.orElse(0) // 0
some.orThrow() // 42
none.orThrow() // throws Error
some.orNull() // 42
none.orNull() // null

Constructors

Method	Description
`Option(value)`	Some if non-null/undefined, else None
`Option.from(value)`	Same as constructor
`Option.none()`	Create None explicitly
`Option.of(value)`	Same as constructor

Transformations

// Map - transform the value if present
Option(5).map((x) => x * 2) // Some(10)
Option(null).map((x) => x * 2) // None

// FlatMap - chain operations that return Options
Option(5).flatMap((x) => (x > 0 ? Option(x) : Option.none()))

// Filter - keep value only if predicate passes
Option(5).filter((x) => x > 3) // Some(5)
Option(5).filter((x) => x > 10) // None

// Tap - side effect without changing value
Option(5).tap((x) => console.log(x)) // logs 5, returns Some(5)

Pattern Matching

// Using fold
const result = Option(user).fold(
  () => "No user found",
  (u) => `Hello, ${u.name}`,
)

// Using match
const greeting = Option(name).match({
  Some: (n) => `Hello, ${n}`,
  None: () => "Hello, stranger",
})

Do-Notation

import { Do, $ } from "functype/do"

const result = Do(function* () {
  const a = yield* $(Option(1))
  const b = yield* $(Option(2))
  const c = yield* $(Option(3))
  return a + b + c
}) // Some(6)

// Short-circuits on None
const failed = Do(function* () {
  const a = yield* $(Option(1))
  const b = yield* $(Option.none<number>()) // stops here
  const c = yield* $(Option(3))
  return a + b + c
}) // None

Key Features

Type Safety: TypeScript enforces explicit handling of empty cases
Chainable Operations: map, flatMap, filter without null checks
Pattern Matching: Explicit Some/None handling with fold() and match()
Composable: Works with Do-notation for complex workflows

When to Use Option

Function return values that might not exist (database queries, array searches)
Optional configuration or parameters
Chaining operations where any step might fail
Replacing nullable types with explicit presence/absence

Type Conversions

option.toEither("Error message") // Left("Error message") or Right(value)
option.toList() // List([]) or List([value])
option.toTry() // Failure or Success(value)
option.toPromise() // Rejected or Resolved Promise

API Reference

See full API documentation at functype API docs

Option<T>