modelico-immutable

Modélico [moˈðe.li.ko] is a universal-JS library for serialisable immutable models.

Note: babel-polyfill might be required for browsers other than Chrome, Firefox and Edge. Additionally, IE 9 & 10 also require a getPrototypeOf polyfill as the one in es5-sham. See browser tests for more details.

Installation

npm i modelico

To use it in the browser, grab the minified or the development files.

Run the current tests directly on your target browsers to see what setup is right for you:

• Run with standard ES5 setup
• Run with legacy ES3 setup

Quick intro

The goal is to parse JSON strings like the following into JavaScript custom objects

{
  "name": "Robbie"
}

so that we can do things like this:

const pet1 = M.fromJSON(Animal, petJson);
 
pet1.speak(); //=> 'my name is Robbie!'
 
// pet1 will not be mutated
const pet2 = pet1.set('name', 'Bane');
 
pet2.name(); //=> 'Bane'
pet1.name(); //=> 'Robbie'

M.fromJSON is a simpler way to do the following:

const { _ } = M.metadata;
const pet1 = JSON.parse(petJson, _(Animal).reviver);

Here is how Animal would look like:

const M = require('modelico');
const { string } = M.metadata;
 
class Animal extends M.Base {
  constructor(fields) {
    super(Animal, fields);
  }
 
  speak() {
    const name = this.name();
 
    return (name === '') ?
      `I don't have a name` :
      `My name is ${name}!`;
  }
 
  static innerTypes() {
    return Object.freeze({
      name: string()
    });
  }
}

A more complex example

The previous example features a standalone class. Let's look at a more involved example that builds on top of that:

{
  "givenName": "Javier",
  "familyName": "Cejudo",
  "pets": [
    {
      "name": "Robbie"
    }
  ]
}

Notice that the data contains a list of pets (Animal).

Again, our goal is to parse JSON into JavaScript classes to be able to do things like

const person1 = M.fromJSON(Person, personJson);
 
person1.fullName(); //=> 'Javier Cejudo'
person1.pets().inner()[0].speak(); //=> 'my name is Robbie!'

Note: pets() returns a Modelico.List, hence the need to use .inner() to grab the underlying array. See the proxies section for a way to use methods and properties of the inner structure directly.

We are going to need a Person class much like the Animal class we have already defined.

const M = require('modelico');
const { _, string, list } = M.metadata;
 
class Person extends M.Base {
  constructor(fields) {
    super(Person, fields);
  }
 
  fullName() {
    return [this.givenName(), this.familyName()].join(' ').trim();
  }
 
  static innerTypes() {
    return Object.freeze({
      givenName: string(),
      familyName: string(),
      pets: list(_(Animal))
    });
  }
}

A note on immutability

Following the examples above:

const person2 = person1.set('givenName', 'Javi');
 
// person2 is a clone of person with the givenName
// set to 'Javi', but person is not mutated
person2.fullName(); //=> 'Javi Cejudo'
person1.fullName(); //=> 'Javier Cejudo'
 
const person3 = person1.setPath(['pets', 0, 'name'], 'Bane');
 
person3.pets().inner()[0].name(); //=> 'Bane'
person1.pets().inner()[0].name(); //=> 'Robbie'

Optional / null values

In the examples above, a pet with a null or missing name would cause a TypeError while reviving.

const pet = M.fromJSON(Animal, '{"name": null}');
//=> TypeError: no value for key "name"

To support missing properties or null values, you can declare the property as a Maybe:

const M = require('modelico');
const { string, maybe } = M.metadata;
 
class Animal extends M.Base {
 
  // ... same as before
 
  static innerTypes() {
    return Object.freeze({
      name: maybe(string())
    });
  }
}

Then, we can use it as follows:

const pet = M.fromJSON(Animal, '{"name": null}');
 
pet.name().isEmpty(); //=> true
pet.name().getOrElse('Bane'); //=> Bane

ES2015 proxies

Most built-in types in Modélico (List, Set, Map, EnumMap and Date) are wrappers around native structures. By default, it is necessary to retrieve those structures to access their properties and methods (eg. list.inner().length).

However, if your environment supports ES2015 proxies, Modélico provides utilities to get around this:

const M = Modelico;
const p = M.proxyMap;
 
const defaultMap = M.Map.fromObject({a: 1, b: 2, c: 3});
const proxiedMap = p(defaultMap);
 
// without proxies
defaultMap.inner().get('b'); //=> 2
defaultMap.inner().size; //=> 3
 
// with proxies
proxiedMap.get('b'); //=> 2
proxiedMap.size; //=> 3

Please note that native methods that modify the structure in place will instead return a new modelico object:

const proxiedMap2 = proxiedMap.delete('b');
 
proxiedMap.size;  //=> 3 (still)
proxiedMap2.size; //=> 2

See proxy tests for more details.

ES5 classes

To support legacy browsers without transpiling, Modélico can be used with ES5-style classes. In the case of our Animal class:

(function(M) {
  var m = M.metadata;
 
  function Animal(fields) {
    M.Base.factory(Animal, fields, this);
  }
 
  Animal.prototype = Object.create(M.Base.prototype);
  Animal.prototype.constructor = Animal;
 
  Animal.prototype.speak = function() {
    var name = this.name();
 
    return (name === '') ?
      "I don't have a name" :
      'My name is ' + name + '!';
  };
 
  Animal.innerTypes = function() {
    return Object.freeze({
      name: m.string()
    });
  }
}(window.Modelico));

Acknowledgments 🙇

Inspired by Immutable.js, Gson and initially designed to cover the same use cases as an internal Skiddoo tool by Jaie Wilson.