option

The option type, also known as the maybe type, for JavaScript

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:

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");
    }
  • some(value).map(func) returns some(func(value))
  • none.map(func) returns none
  • some(value).toArray() returns [some]
  • none.toArray() returns []

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

If other is a function:

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

If other is not a function:

  • some(value).orElse(other) returns value
  • none.orElse(other) returns other
npm install option