Class: Just

Extends

• Maybe

Methods

staticJust.from(value){Maybe}

data/Maybe.js, line 919

Creates a new Just from a value. If the value is already a Maybe instance, the value is returned unchanged. Otherwise, a new Just is made with the value.

Name	Type	Description
value	*	Value to wrap in a Just.

Returns:

Type	Description
Maybe	Maybe when is the value already wrapped or Just wrapped value.

Examples

Just from nothing

Just.from();
// => Just()

Just from arbitrary value

Just.from(true);
// => Just(true)

Just from another Just

Just.from(Just.from(value));
// => Just(value)

Just from Nothing

Just.from(Nothing.from());
// => Nothing()

inherited abstractap(other){Maybe}

data/Maybe.js, line 315

Applies the function contained in the instance of a Just to the value contained in the provided Just, producing a Just containing the result. If the instance is a Nothing, the result is the Nothing instance. If the instance is a Just and the provided Maybe is Nothing, the result is the provided Nothing.

Name	Type	Description
other	Maybe	Value to apply to the function wrapped in the Just.

Returns:

Type	Description
Maybe	Just wrapped applied function or Nothing.

Example

Just#ap

const findPerson = curryN(3, Person.find); // Person.find(name, birthdate, address)

Just.from(findPerson) // => Just(findPerson)
  .ap(Just.ofNullable(name)) // => Just(name)
  .ap(Just.ofNullable(birthdate)) // => Just(birthdate)
  .ap(Just.ofNullable(address)) // => Just(address)
  .ifJust(console.log); // => Log Person.find() response

inherited abstractchain(method){Maybe}

data/Maybe.js, line 337

Applies the provided function to the value contained for a Just. The function should return the value wrapped in a Maybe. If the instance is a Nothing, the function is ignored and then instance is returned unchanged.

Name	Type	Description
method	Chain.<Maybe>	The function to invoke with the value.

Returns:

Type	Description
Maybe	Maybe wrapped value returned by the provided method.

Example

Just#chain

// Using lodash/fp/curry and get
const getConfigOption = curry((path, config) => Maybe.ofNullable(get(path, config));

Maybe.ofNullable(config)
  .chain(getConfigOption("path.to.option"))

inherited equals(other){Boolean}

data/Maybe.js, line 376

Determines whether or not the other is equal in value to the current (this). This is not a reference check.

Name	Type	Description
other	*	Other value to check.

Returns:

Type	Description
Boolean	true if the two Maybes are equal; false if not equal.

Examples

Reflexivity

v1.equals(v1) === true;
// => true

Symmetry

v1.equals(v2) === v2.equals(v1);
// => true

Transitivity

(v1.equals(v2) === v2.equals(v3)) && v1.equals(v3)
// => true

inherited abstractextend(){Maybe}

data/Maybe.js, line 380

Extends the Maybe. This is used for workflow continuation where the context has shifted.

Type	Description
Extend.<Maybe>	method - The function to invoke with the value.

Returns:

Type	Description
Maybe

Example

Workflow continuation

// Workflow from makeRequest.js
const makeRequest = requestOptions => requestAsPromise(requestOptions)
  .then(Just.from)
  .catch(Nothing.from);

// Workflow from savePerson.js
const savePerson = curry((requestOptions, optionalPerson) => optionalPerson
  .map(Person.from)
  .map(person => set("body", person, requestOptions))
  .map(makeRequest)
);

// Workflow from processResponse.js
const processResponse = optionalResponse => optionalResponse
  .ifJust(console.log);

Maybe.ofNullable(person)
  .extend(savePerson({ method: "POST" }))
  .extend(processResponse);

inherited get(){*}

data/Maybe.js, line 411

Returns the value if the instance is a Just otherwise the null.

Returns:

Type	Description
*

Examples

Just#get

Just.from(value).get();
// => value

Nothing#get

Nothing.from().get();
// => null

inherited abstractifJust(method){Maybe}

data/Maybe.js, line 431

Applies the provided function to the value contain for a Just. Any return value from the function is ignored. If the instance is a Nothing, the function is ignored and the instance is returned.

Name	Type	Description
method	Consumer	The function to invoke with the value.

Returns:

Type	Description
Maybe	Current instance.

Examples

Just#ifJust

Just.from(value).ifJust(doSomething); // doSomething(value)
// => Just(value)

Nothing#ifJust

Nothing.from().ifJust(doSomething); // void
// => Nothing()

inherited abstractifNothing(method){Maybe}

data/Maybe.js, line 451

Applies the provided function to the value contain for a Nothing. Any return value from the function is ignored. If the instance is a Just, the function is ignored and the instance is returned.

Name	Type	Description
method	Callable	The function to invoke.

Returns:

Type	Description
Maybe	Current instance.

Examples

Just#ifNothing

Just.from(value).ifNothing(doSomething); // void
// => Just(value)

Nothing#ifNothing

Nothing.from().ifNothing(doSomething); // doSomething()
// => Nothing()

inherited isJust(){Boolean}

data/Maybe.js, line 501

Determines whether or not the instance is a Just.

Returns:

Type	Description
Boolean	true if the instance is a Just; false is not.

Examples

Just

Just.from(value).isNothing();
// => true

Nothing#isJust

Nothing.from().isNothing();
// => false

inherited isNothing(){Boolean}

data/Maybe.js, line 484

Determines whether or not the instance is a Nothing.

Returns:

Type	Description
Boolean	true if the instance is a Nothing; false is not.

Examples

Just#isNothing

Just.from(value).isNothing();
// => false

Nothing#isNothing

Nothing.from().isNothing();
// => true

inherited abstractmap(method){Maybe}

data/Maybe.js, line 505

Applies the provided function to the value contained for a Just which is, in turn, wrapped in a Just. If the instance is a Nothing, the function is ignored and then instance is returned unchanged.

Name	Type	Description
method	function	The function to invoke with the value.

Returns:

Type	Description
Maybe	Maybe wrapped value mapped with the provided method.

Example

// Using lodash/fp/flow and sort
Just.from([1, 3, 2]).map(flow(sort, join(", ")));
// => Just("1, 2, 3")

Nothing.from().map(flow(sort, join(", ")));
// => Nothing()

inherited of()

data/Maybe.js, line 528

See:

• Maybe.ofNullable

inherited abstractorElse(method){*}

data/Maybe.js, line 532

Returns the value if the instance is a Just otherwise returns the value supplied if the instance is a Nothing.

Name	Type	Description
method	Consumer	The function to invoke with the value.

Returns:

Type	Description
*

Examples

Just#orElse

Just.from(value).orElse(otherValue);
// => value

Nothing#orElse

Nothing.from().orElse(otherValue);
// => otherValue

inherited abstractorElseGet(method){*}

data/Maybe.js, line 552

Return the value if the instance is a Just otherwise returns the value from the function provided.

Name	Type	Description
method	Supplier	The function supplying the optional value.

Returns:

Type	Description
*

Examples

Just#orElseGet

Just.from(value).orElseGet(getOtherValue);
// => value

Nothing#orElseGet

Nothing.from().orElseGet(getOtherValue);
// => otherValue

inherited abstractorElseThrow(method){*}

data/Maybe.js, line 571

Returns the value if the instance is a Just otheriwse throws the Error supplied by the function provided.

Name	Type	Description
method	Supplier	The function to invoke with the value.

Throws:

returned by the provided function.

Type

Error

Returns:

Type	Description
*

Examples

Just#orElseThrow

Just.from(value).orElseThrow(createException);
// => value

Nothing#orElseThrow

Nothing.from().orElseThrow(createException); // throw createException()

inherited abstracttoEither(either){Either}

data/Maybe.js, line 591

Converts the Maybe to an Either. Just becomes a Right and Nothing becomes a Left.

Name	Type	Description
either	Either	Either implementation.

Returns:

Type	Description
Either	Either wrapped value.

Examples

Just#toEither

const Either = require("lodash-fantasy/data/Either");

Just.from(value).toEither(Either);
// => Either.Right(value);

Nothing#toEither

const Either = require("lodash-fantasy/data/Either");

Nothing.from().toEither(Either);
// => Either.Left(null);

inherited abstracttoPromise(promise){Promise}

data/Maybe.js, line 615

Converts the Maybe to a Promise using the provided Promise implementation.

Name	Type	Description
promise	Promise	Promise implementation.

Returns:

Type	Description
Promise	Promise wrapped value.

Examples

Just#toPromise

const Bluebird = require("bluebird");

Just.from(value).toPromise(Bluebird);
// => Promise.resolve(value);

Nothing#toPromise

const Bluebird = require("bluebird");

Nothing.from().toPromise(Bluebird);
// => Promise.reject(null);

inherited abstracttoString(){String}

data/Maybe.js, line 638

Returns a String representation of the Maybe.

Returns:

Type	Description
String	String representation.

Examples

Just#toString

Just.from(1).toString();
// => "Maybe.Just(1)"

Nothing#toString

Nothing.from().toString();
// => "Maybe.Nothing(null)"

inherited abstracttoValidation(validation){Validation}

data/Maybe.js, line 656

Converts the Maybe to an Validation. Just becomes a Success and Nothing becomes a Failure.

Name	Type	Description
validation	Validation	Validation implementation.

Returns:

Type	Description
Validation	Validation wrapped value.

Examples

Just#toValidation

const Validation = require("lodash-fantasy/data/Validation");

Just.from(value).toValidation(Validation);
// => Validation.Success(value);

Nothing#toValidation

const Validation = require("lodash-fantasy/data/Validation");

Nothing.from().toValidation(Validation);
// => Validation.Failure([null]);