Fully Typed Option Library - (Tutorial)

A TypeScript implementation of Option. Based on Scala's Option library.

Options force the user to always ensure they are handling for the possible null case. By defining optional method parameters as options you can keep a more consistent syntax and ensure the method implementation stays compatible with both possibilities.

Options keep with the iterable api, meaning you can duck type the with arrays, streams, ect.

Options also ensure a more functional approach to programming, and help keep code cleaner and easier to read.

With TypeScript this becomes awesome, because youa re able to ensure that all null cases are handled at compile time.

Bower and Npm

npm install cs-option bower install cs-option

How to use:

There are both helper static members and instance members listed below. Also for more information see my blog post on the subject, where we go over example uses.

Static Members:

isNully(possiblyUndefinedOrNullValue: any): boolean;

Helper to check if a variable is null or undefined.

Option.isNully(undefined) // => true
Option.isNully(null) // => true

Option.isNully(0) // => false
Option.isNully("") // => false
Option.isNully(1) // => false
Option.isNully([]) // => false

fromNullable<T>(possiblyUndefinedOrNullValue: T | undefined): Option<T>

Used to create an option out of any value, even possibly null values. Useful when calling an untrusted api like array.pop since it could return a value or undefined.

Option.fromNullable(possiblyACat) // => Option[possiblyACat]

of<T>(value: T): Option<T>

Makes an option out of a concrete value. Useful when calling an api that expects an option, but you have a value.

Option.of(1)

find<T>(arr: T[], fnOrMatch?: LodashMatches<T>): Option<T>

Wraps array.find so that it returns an option. If you have lodash included it is much more flexable with the second parameter.

Option.find(arrayOfNumber, (num) => num === 1) // Option[1]

pop<T>(arr: T[]): Option<T>

Wraps array.pop in an Option.

Option.pop(arr) // => Option[value] || Option[undefined]

absent<T>(): Option<T>

Generates an empty option.

Option.absent<number>() // Option[undefined] 

Instance Members:

isPresent(): boolean

Checks if the Options has a value.

Option.of(1).isPresent() // => true
Option.fromNullable(null).isPresent() // => false

isAbsent(): boolean

Checks if the Options does not have a value.

Option.of(1).isAbsent() // => false
Option.fromNullable(null).isAbsent() // => true

get(): T

Gets the options value, and throws an error if absent.

Option.of(1).get() // => 1
Option.fromNullable(null).get() // => throw

or(orValue: T): T

Returns the options value or a default value

Option.of(1).or(2) // => 1
Option.fromNullable(null).or(2) // => 2

orThrow(error: (typeof Error) | string, message?: string): T

Option.of(1).orThrow("we need a value") // => 1
Option.of(1).orThrow(Error, "we need a value") // => 1
Option.fromNullable(null).orThrow("we need a value") // => throw "we need a value"

forEach(fn: (value: T) => any): void

If the option is nonempty calls the callback on it, else do nothing. "forEach" might seem odd for a singleton, but this is consistent with Scala's Option, and keeps with the iterable terminology

Option.of(1).forEach(num => console.log(num)) // => 1
Option.fromNullable(null).forEach(num => console.log(num)) //

orCall(fn: () => T): T

Returns the option's value if present otherwise calls the callback and returns its return

Option.of(1).orCall(() => 2) // => 1
Option.fromNullable(null).orCall(() => 2) // => 2
Option.fromNullable(null).orCall(() => {throw "something"}) // throw "something"

orElse(alternative: Option<T>): Option<T>

If the option is nonempty return it, otherwise return the result of evaluating an alternative expression.

Useful when you need a default but the method api you are passing it to needs an option.

Option.of(1).orElse(Option.of(1)) // => Option[1]
Option.fromNullable(null).orElse(Option.fromNullable(undefined)) // => Option[undefined]

filter(is: (value: T) => boolean): Option<T>

Returns this $option if it is nonempty and applying the predicate $p to this $option's value returns true. Otherwise, return $none.

Useful when you have an object that needs to be filtered on a value.

Option.of(1).filter(n => n === 1) // => Option[1]
Option.of(2).filter(n => n === 1) // => Option[undefined]
Option.fromNullable(null).filter(n => n === 1) // => Option[undefined]

filterValue(is: T): Option<T>

Returns this $option if it is nonempty and is true when the predicate $p is compared with strict equality to this $option's value returns true. Otherwise, return $none.

Option.of(1).filterValue(1) // => Option[1]
Option.of(2).filterValue(1) // => Option[undefined]
Option.fromNullable(null).filterValue(1) // => Option[undefined]

filterNotValue(is: T): Option<T>

Returns this $option if it is nonempty and is false when the predicate $p is compared with strict equality to this $option's value returns true. Otherwise, return $none.

Option.of(1).filterNotValue(1) // => Option[undefined]
Option.of(2).filterNotValue(1) // => Option[1]
Option.fromNullable(null).filterNotValue(1) // => Option[undefined]

contains(elem: T): boolean

Tests whether the option contains a given value as an element.

Option.of(1).contains(1) // => true
Option.of(2).contains(1) // => false
Option.fromNullable(null).contains(1) // => false

exists(is: (value: T) => boolean): boolean

Returns true if this option is nonempty and the predicate $p returns true when applied to this $option's value. Otherwise, returns false.

Option.of(1).exists(n => n === 1) // => true
Option.of(2).exists(n => n === 1) // => false
Option.fromNullable(null).exists(n => n === 1) // => false

map<V>(transformer: (value: T) => V): Option<V>

Transform an option into another option

Option.of(1).map(n => n * 2) // => Option[2]
Option.of(2).map(n => n * 2) // => Option[4]
Option.of({name: "Blue"}).map(n => n.name) // => Option["Blue"]
Option.fromNullable(null).map(n => n * 2) // => Option[undefined]

flatMap<V>(transformer: (value: T) => Option<V>): Option<V>

Transfrom an option into another option while flattening nesting.

Option.of({name: Option.of("Blue")}).flatMap(n => n.name) // => Option["Blue"]
Option.fromNullable(null).flatMap(n => n.name) // => Option[undefined]

promiseTransform<V>(q: PromiseConstructor, transformer: (value: T) => Promise<V>): Promise<Option<V>>

Takes in a promise constructor to map an option into a promise wrapped option.

Option.of(user).promiseTransform(Promise /* or $q */, saveUser) // => user saved and user data returned Promise[Option[user]]
Option.fromNullable(possibleUser /* null in this example */).promiseTransform(Promise /* or $q */, saveUser) // => user saved and user data returned Promise[Option[user]]