NOTE

This project is no longer actively supported. If anyone is interested in becoming the new maintainer, don't hesitate to contact me (hughfdjackson@googlemail.com).

The go-to immutable library is https://github.com/facebook/immutable-js.

immutable

Effecient immutable collections in javascript.

Why?

Using immutable objects can make code easier to reason about, allowing programmers to geniunely create sections of their programs that operate on a 'data-in/data-out' basis.

This style of code is easy to test, and use in a mix-and-match style.

Install

npm

npm install immutable

browser

Download build/immutable.js, and include it as a script tag.

AMD/require.js

Download build/immutable.js, and require it in:

require(['libs/immutable'], function(immutable){
  // ... assuming immutable is in libs/immutable.js, now it's ready to use
})

Usage

Immutable has two types of collection: objects and arrays. Like regular JavaScript Objects and Arrays, both act as key:value stores (using strings as the keys).

Basic Manipulation

creation

var person = im.object({ name: 'joe bloggs', age: 34 })
var numbers = im.array([1, 2, 3, 4, 5])

.assoc

var emptyObj = im.object()
var person = emptyObj.assoc({ name: 'joe bloggs', age: 34 })
var personWithSports = person.assoc('sport', 'golf')

var emptyArr = im.array()
var numbers = emptyArr.assoc([1, 2, 3, 4, 5])
var upTo6 = numbers.assoc(5, 6)

.get

var person = im.object({ name: 'joe bloggs', age: 34 })
person.get('age') //= 34

var numbers = im.array([1, 2, 3, 4, 5])
numbers.get(0) //= 1

.has

var person = im.object({ name: 'joe bloggs', age: 34 })

person.has('name')        //= true
person.has('discography') //= false

.dissoc

Create a collection like this one, but without a particular property:

var person = im.object({ name: 'joe bloggs', age: 34 })
var personShyAboutAge = person.dissoc('age')

personShyAboutAge.has('age') //= false

var numbers = im.array([1, 2, 3, 4, 5])
var upTo4 = numbers.dissoc(4) // dissocs the 4th key

numbers.has(4) //= true
upTo4.has(4)   //= false

.mutable / .toJSON

Create a regular JavaScript object from an immutable one:

var person = im.object({ name: 'joe bloggs', age: 34 })
person.mutable() //= { name: 'joe bloggs', age: 34 }

The .toJSON alias allows immutable objects to be serialised seamlessly with regular objects:

var favouritePeople = {
	joe: im.object({ name: 'joe bloggs', age: 34, sports: im.array(['golf', 'carting']) })
}

JSON.stringify(favouritePeople) // = '{ "joe": { "name": "joe bloggs", "age": 34, "sports": ["golf", "carting"] } }'

Value Equality

Collections can be checked for equality:

var person1 = im.object({ name: 'joe bloggs', age: 34 })
var person2 = im.object({ name: 'joe bloggs', age: 34 })
var person3 = im.object({ name: 'joe bloggs', age: 34, sport: 'golf' })

person1.equal(person2) //= true
person3.equal(person2) //= false

Collections are considered equal when:

• They are immutable
• They have all the same keys
• All values are: ** Mutable objects or primtive values that are strictly equal (===), ** Immutable objects that are .equal to one another

Iteration methods

Immutable objects and arrays can be iterated over almost identically, except that:

• objects iterate over all keys, and return objects where appropriate;
• arrays iterate over only numberic keys, and return arrays where appropriate.

All iterator methods (unless mentioned) will pass the value, the key, and the original immutable object to their callback functions.

.map

var inc = function(a){ return a + 1 }

var coordinates = im.object({ x: 1, y: 1 })
coordinates.map(inc).mutable() //= { x: 2, y: 3 }

var numbers = im.array([1, 2, 3, 4, 5])
numbers.map(inc).mutable() //= [2, 3, 4, 5, 6]

.forEach

var log = console.log.bind(console)

var person = im.object({ name: 'joe bloggs', age: 34 })
person.map(log)
// *log output*
// 'joe bloggs' 'name' person
// 34           'age'  person

.filter

var isNum = function(a){ return typeof a === 'number' }

var person = im.object({ name: 'joe bloggs', age: 34 })
person.filter(isNum).mutable() //= { age: 34 }

var alphaNumber = im.array(['a', 1, 'b', 2, 'c', 3])
alphaNumber.filter(isNum).mutable() //= [1, 2, 3]

.every

var isNum = function(a){ return typeof a === 'number' }

im.object({ name: 'joe bloggs', age: 34 }).every(isNum) //= false
im.object({ x: 1, y: 2 }).every(isNum) //= true

im.array(['a', 1, 'b', 2, 'c', 3]).every(isNum) //= false
im.array([1, 2, 3]).every(isNum) //= true

.some

var isNum = function(a){ return typeof a === 'number' }

im.object({ name: 'joe bloggs', sport: 'golf' }).some(isNum) //= false
im.object({ name: 'joe bloggs', age: 34 }).some(isNum) //= true

im.array(['a', 'b', 'c']).some(isNum) //= false
im.array(['a', 1, 'b', 2, 'c', 3]).every(isNum) //= true

.reduce

var flip = function(coll, val, key){
	return coll.assoc(key, val)
}

var coords = im.object({ x: '1', y: '2', z: '3' })
var flippedCoords = coords.reduce(flip, im.object())
flippedCoords.mutable() //= { 1: 'x', 2: 'y', 3: 'z' }

var cat = function(a, b){ return a + b }
var letters = im.array(['a', 'b', 'c'])
letters.reduce(cat)  //= 'abc'

Array Methods

Since arrays are ordered collections, they have some methods of their own, that only make sense in an ordered context:

.reduceRight

var cat = function(a, b){ return a + b }
var letters = im.array(['a', 'b', 'c'])
letters.reduceRight(cat)  //= 'cba'

.push

var numbersTo3 = im.array([1, 2, 3])
var numbersTo4 = numbersTo3.push(4)

numbersTo4.mutable() //= [1, 2, 3, 4]

.indexOf

var mixed = im.array([1, 2, 3, im.object({ x: 3 }), { x: 3 }])
mixed.indexOf('a')      //= -1 -- 'a' not in array
mixed.indexOf({ x: 3 }) //= -1 -- mutable objects are compared by reference
mixed.indexOf(im.object({ x: 3 })) //= 3 -- immutable objects are compared by value
mixed.indexOf(3) //= 2 -- primitives are compared by value

Library Functions

.isImmutableCollection

A predicate that returns true if the object is an immutable one, such as produced by this library.

im.isImmutableCollection(im.array([1, 2, 3])) //= true
im.isImmutableCollection(Object.freeze({}))   //= false - you couldn't assoc/dissoc/get/set on it