options for node.js

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:

``javascript
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.

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

Methods

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

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

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

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Conventionally used when func returns another option.

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

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* some(value).filter(predicate) returns:
* some(value) if predicate(value) === true
* none if predicate(value) === false
* none.filter(predicate) returns none

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

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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

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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

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

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* 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

npm install option