An implementation of the option type, sometimes known as the maybe type.

An instance of an option type is an optional value. Either it's none, or an instance of Some:

var option = require("option");

var some = option.some("Bob");
var none = option.none;

A function that returns an optional string isn't that different from a function that returns a string or null. The advantage over null is that options provide a number of functions that help with manipulating optional values.

    function greet(user) {
        return "Hello " + user.name().valueOrElse("Anonymous");
    }

Methods

isNone() and isSome()

• some(value).isNone() returns false
• some(value).isSome() returns true
• none.isNone() returns true
• none.isSome() returns false

value()

• some(value).value() returns value
• none.value() throws an error

map(func)

• some(value).map(func) returns some(func(value))
• none.map(func) returns none

flatMap(func)

• some(value).flatMap(func) returns func(value)
• none.flatMap(func) returns none

toArray()

• some(value).toArray() returns [some]
• none.toArray() returns []

orElse(other)

If other is a function (other conventionally returning another option):

• some(value).orElse(other) returns some(value)
• none.orElse(other) returns other()

If other is not a function (other conventionally being another option):

• some(value).orElse(other) returns some(value)
• none.orElse(other) returns other

valueOrElse(other)

If other is a function:

• some(value).valueOrElse(other) returns value
• none.valueOrElse(other) returns other()

If other is not a function:

• some(value).valueOrElse(other) returns value
• none.valueOrElse(other) returns other

Functions

option.isOption(value)

• option.isOption(value) returns true if value is option.none or option.some(x).

option.fromNullable(value)

• If value is null or undefined, option.fromNullable(value) returns option.none.
• Otherwise, returns option.some(value). For instance, option.fromNullable(5) returns option.some(5).

Installation