Option structure in JavaScript

Installation and usage

npm install --save possibly

Usage in Node

/* require */
var Possibly = require('possiblt');
var Some = Possibly.Some;
var None = Possibly.None;

/* use */
var someOpt = Possibly.Some('value');
var noneOpt = Possibly.None();

Usage in browser

/* add script tag and use global variable 'Possibly' */
var Some = Possibly.Some;
var None = Possibly.None;

/* use */
var someOpt = Possibly.Some('value');
var noneOpt = Possibly.None();

Usage in browser with RequireJS

require(['possibly'], function(Possibly) {
    var Some = Possibly.Some;
    var None = Possibly.None;

    /* use */
    var someOpt = Possibly.Some('value');
    var noneOpt = Possibly.None();
})

Create new option type

var someOpt = Some('value');
var noneOpt = None();

Is it Some or None?

someOpt.isSome()  // true
someOpt.isNone()  // false
noneOpt.isSome()  // false
noneOpt.isNone()  // true

Possibly.isSome(someOpt)    // true
Possibly.isNone(someOpt)    // false
Possibly.isSome(noneOpt)    // false
Possibly.isNone(noneOpt)    // true

Possibly.isSome("I'm not Some")         // false
Possibly.isNone("I'm not None")         // false
Possibly.isOption("And I'm not Option") // false
Possibly.isOption(Some("But I am"))     // true

Access the value

someOpt.valueOf()  // 'value'
noneOpt.valueOf()  // undefined

Access the value, or else...

someOpt.valueOrElse('default value')  // 'value'
noneOpt.valueOrElse('default value')  // 'default value'

Map, filter, every, forEach...

/* Map */
someOpt.map(function(value) {
  return value.toUpperCase()
});
// => 'VALUE'

noneOpt.map(function(value) {
  return value.toUpperCase()
});
// => undefined

/* TODO Filter */
someOpt.filter(function(value) {
  return value !== ''
});
// => 'value'

noneOpt.filter(function(value) {
  return value !== ''
});
// => 'null'

/* TODO Each */
someOpt.forEach(function(value) {
  alert(value);
});
// => alerts 'value'

noneOpt.forEach(function(value) {
  alert(value);
});
// => does not alert

Wait, what? Map, filter, every and co. are array methods. How do they apply to Option structure?

Think Option as an array with either one or none elements. E.g. map over Some is same as mapping over an array with only one element. Similarly, map over None is same as mapping over an array with no elements. And in fact, the Option library doesn't implement its own map, filter etc. methods, instead it uses native array methods.

Following array methods are supported:

• map
• filter
• forEach
• every
• sort
• reverse
• forEach
• every
• some
• reduce
• reduceRight
• join
• slice
• lastIndexOf
• concat
• indexOf