linusnorton/ts-option

ts-option

Scala like Option type for TypeScript/JavaScript.

Install

$ npm install --save ts-option

Usage

TypeScript

import {Option, option, some, none} from "ts-option";

let a: Option<number> = option(1);    // Some(1)
let c: Option<number> = some(2);      // Some(2)
let b: Option<number> = option(null); // None
let d: Option<number> = none;         // None

JavaScript (ES2015/ES6)

import {Option, option, some, none} from "ts-option";

let a = option(1);    // Some(1)
let c = some(2);      // Some(2)
let b = option(null); // None
let d = none;         // None

API

option<A>(valiue: A): Option<A>

Create an Option instance from a value. It returns Some<A> when the value is not null/undefined, otherwise returns None.

some<A>(value: A): Some<A>

Create an Some instance from a value. It returns Some<A> even if the value is null or undefined.

none: None

The None type singleton object.

option<A>(...).exists(p: (_: A) => boolean): boolean

Returns true if the option is non-empty and the predicate p returns true when applied to the option's value.

option<A>(...).filter(p: (_: A) => boolean): Option<A>

Returns the option if it is non-empty and applying the predicate p to the option's value returns true.

option<A>(...).filterNot(p: (_: A) => boolean): Option<A>

Returns the option if it is non-empty and applying the predicate p to the option's value returns false.

option<A>(...).flatMap<B>(f: (_: A) => Option<B>): Option<B>

Returns the result of applying f to the option's value if the option is non-empty, otherwise returns None.

option<A>(...).fold<B>(ifEmpty: () => B)(f: (_: A) => B): B

Returns the result of applying f to the option's value if the option is non-empty, otherwise returns ifEmpty value.

option<A>(...).forAll(p: (_: A) => boolean): boolean

Tests whether a predicate holds for all elements of the option.

option<A>(...).forEach(f: (_: A) => any): void

Apply the given procedure f to the option's value if it is non-empty, otherwise do nothing.

option<A>(...).get: A

Returns the option's value if the option is non-empty, otherwise throws an error.

option<A>(...).getOrElse(defaultValue: A | (() => A)): A

Returns the option's value if the option is non-empty, otherwise return the result of evaluating default.

option<A>(...).isDefined: boolean

Returns true if the option's value is non-empty, false otherwise.

option<A>(...).isEmpty: boolean

Returns true if the option's value is empty, false otherwise.

option<A>(...).map<B>(f: (_: A) => B): Option<B>

Builds a new option by applying a function to all elements of this option.

option<A>(...).match<B>(m: {some: (_: A) => B, none: () => B}): B

Scala's "Pattern Match" like signature. Returns the value that the function some returns if the option is non-empty, otherwise returns the value that function none returns.

let s: Option<number> = some(9);
let n: Option<number> = none;

let a: number = s.match({
  some: x => x * 9,
  none: () => -1,
});
let b: number = n.match({
  some: x => x * 9,
  none: () => -1,
});

console.log(a); // 81
console.log(b); // -1

option<A>(...).nonEmpty: boolean

Returns true if the option is an instance of Some, false otherwise.

option<A>(...).orElse(alternative: () => Option<A>): Option<A>

Returns the option itself if it is non-empty, otherwise return the result of evaluating alternative.

option<A>(...).orNull: A

Returns the option's value if it is non-empty, or null if it is empty.

option<A>(...).toArray: Array<A>

Converts the option to an array.

option<A>(...).forComprehension(...fns: (a: any) => Option<any>): Option<any>

Performs a for-comprehension like operation using the given list of functions. For example:

const nestedOptions = some({
  anOption: some({
    anotherOption: some({
      finalValue: true
    })
  })
});

const result = nestedOptions.forComprehension(
  obj => obj.anOption,
  anOption => anOption.anotherOption,
  anotherOption => anotherOption.finalValue
);

// result = option(true)

As with the Scala for comprehension the result of each function is flat-mapped with the next, except for the last, which is mapped.

Please note that there are currently some limitations:

1. Filtering must be done manually
2. There is no shared scope between functions
3. The result type is always Option<any>

License

MIT