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https://github.com/ds300/derivablejs

Functional Reactive State for JavaScript and TypeScript
https://github.com/ds300/derivablejs

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Functional Reactive State for JavaScript and TypeScript

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README 

        
DerivableJS


State made simple → Effects made easy



## [![npm](https://img.shields.io/npm/v/derivable.svg?maxAge=2592000)](https://www.npmjs.com/package/derivable) [![Build Status](https://travis-ci.org/ds300/derivablejs.svg?branch=new-algo)](https://travis-ci.org/ds300/derivablejs) [![Coverage Status](https://coveralls.io/repos/github/ds300/derivablejs/badge.svg?branch=new-algo)](https://coveralls.io/github/ds300/derivablejs?branch=new-algo) [![Join the chat at https://gitter.im/ds300/derivablejs](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/ds300/derivablejs?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge) [![Empowered by Futurice's open source sponsorship program](https://img.shields.io/badge/sponsor-chilicorn-ff69b4.svg)](http://futurice.com/blog/sponsoring-free-time-open-source-activities?utm_source=github&utm_medium=spice&utm_campaign=derivablejs) [![.min.gz size](https://img.shields.io/badge/.min.gz%20size-3.4k-blue.svg)](http://github.com)



Derivables are an Observable-like state container with superpowers. Think

[MobX](https://github.com/mobxjs/mobx) distilled to a potent essence, served

with two heaped tablespoons of extra performance, a garnish of declarative

effects management, and a healthy side-salad of immutability.



* [Quick start](#quick-start)

* [Reactors](#reactors)

* [Key differences with MobX](#key-differences-with-mobx)

* [API / Documentation](#api--documentation)

* [Usage](#usage)

  * [With React](#with-react)

  * [With Immutable](#with-immutable)

  * [Debugging](#debugging)

  * [Examples](#examples)

* [Contributing](#contributing)

* [Inspiration <3](#inspiration-3)

* [License](#license)



## Quick start



There are two types of Derivable:



* **Atoms**



  Atoms are simple mutable references to immutable values. They represent the

  ground truth from which all else is derived.



  ```js

  import { atom } from "derivable";



  const name = atom("Richard");



  name.get(); // => 'Richard'



  name.set("William");



  name.get(); // => 'William'

  ```



* **Derivations**



  Derivations are declarative transformations of values held in atoms. You can

  create them with the `derive` function.



  ```js

  import { derive } from "derivable";



  const cyber = word =>

    word

      .toUpperCase()

      .split("")

      .join(" ");



  const cyberName = derive(() => cyber(name.get()));



  cyberName.get(); // 'W I L L I A M'



  name.set("Sarah");



  cyberName.get(); // 'S A R A H'

  ```



  Unlike atoms, derivations cannot be modified in-place with a `.set` method.

  Their values change only when one or more of the values that they depend upon

  change. Here is an example with two dependencies.



  ```js

  const transformer = atom(cyber);



  const transformedName = derive(() => transformer.get()(name.get()));



  transformedName.get(); // => 'S A R A H'



  const reverse = string =>

    string

      .split("")

      .reverse()

      .join("");



  transformer.set(reverse);



  transformedName.get(); // => 'haraS'



  name.set("Fabian");



  transformedName.get(); // => 'naibaF'

  ```



  `derive` takes a function of zero arguments which should dereference one or

  more Derivables to compute the new derived value. DerivableJS then sneakily

  monitors who is dereferencing who to infer the parent-child relationships.



## Reactors



Declarative state management is nice in and of itself, but the real benefits

come from how it enables us to more effectively manage side effects. DerivableJS

has a really nice story on this front: changes in atoms or derivations can be

monitored by things called **Reactors**, which do not themselves have any kind

of 'current value', but are more like independent agents which exist solely for

executing side effects.



Let's have a look at a tiny example app which greets the user:



```js

import { atom, derive, transact } from "derivable";



// global application state

const name = atom("World"); // the name of the user

const countryCode = atom("en"); // for i18n



// static constants don't need to be wrapped

const greetings = {

  en: "Hello",

  de: "Hallo",

  es: "Hola",

  cn: "您好",

  fr: "Bonjour"

};



// derive a greeting message based on the user's name and country.

const greeting = derive(() => greetings[countryCode.get()]);

const message = derive(() => `${greeting.get()}, ${name.get()}!`);



// set up a Reactor to print the message every time it changes, as long as

// we know how to greet people in the current country.

message.react(msg => console.log(msg), { when: greeting });

// $> Hello, World!



countryCode.set("de");

// $> Hallo, World!

name.set("Dagmar");

// $> Hallo, Dagmar!



// we can avoid unwanted intermediate reactions by using transactions

transact(() => {

  countryCode.set("fr");

  name.set("Étienne");

});

// $> Bonjour, Étienne!



// if we set the country code to a country whose greeting we don't know,

// `greeting` becomes undefined, so the `message` reactor won't run

// In fact, the value of `message` won't even be recomputed.

countryCode.set("dk");

// ... crickets chirping

```



The structure of this example can be depicted as the following DAG:






## Key differences with MobX



* Smaller API surface area.



  There are far fewer _kinds of thing_ in DerivableJS, and therefore fewer

  things to learn and fewer surprising exceptions and spooky corners. This

  reduces noise and enhances one's ability to grok the concepts and wield the

  tools on offer. It also shrinks the set of tools on offer, but maybe that's

  not a bad thing:



  > It seems that perfection is attained not when there is nothing more to add,

  > but when there is nothing more to remove.



  _- Antoie de Saint Exupéry_



* No transparent dereferencing and assignment.



  It is always necessary to call `.get` on derivables to find out what's inside,

  and you always have to call `.set` on atoms to change what's inside. This

  provides a consistent semantic and visual distinction between ordinary values

  and derivable values.



* No observable map and array types.



  So you probably have to use something extra like Immutable,

  [icepick](https://github.com/aearly/icepick) or

  [pure javascript immutable arrays](https://vincent.billey.me/pure-javascript-immutable-array/)

  to deal with collections. Not great if you're just out to get shit done fast,

  but the benefits of immutable collections become more and more valuable as

  projects mature and grow in scope.



* More subtle control over reactors



  DerivableJS has a tidy and flexible declarative system for defining when

  reactors should start and stop. This is rather nice to use for managing many

  kinds of side effects.



* Speed



  DerivableJS is finely tuned, and propagates change significantly faster than

  MobX. \[link to benchmark-results.html forthcoming\]



## API / Documentation



[Over Here](https://ds300.github.io/derivablejs)



## Usage



DerivableJS is fairly mature, and has been used enough in production by various

people to be considered a solid beta-quality piece of kit.



### With React



The fantastic project

[react-derivable](https://github.com/andreypopp/react-derivable) lets you use

derivables in your render method, providing seamless interop with

component-local state and props.



### With Immutable



DerivableJS works spiffingly with

[Immutable](https://github.com/facebook/immutable), which is practically

required if your app deals with medium-to-large collections.



### Debugging



Due to inversion of control, the stack traces you get when your derivations

throw errors can be totally unhelpful. There is a nice way to solve this problem

for dev time. See

[setDebugMode](https://ds300.github.com/derivablejs/#derivable-setDebugMode) for

more info.



### Examples



[See here](https://github.com/ds300/derivablejs/tree/master/examples)



## Contributing



I heartily welcome questions, feature requests, bug reports, and general

suggestions/criticism on the github issue tracker. I also welcome bugfixes via

pull request (please read CONTRIBUTING.md before sumbmitting).



## Inspiration <3



* [Are we there yet?](https://www.infoq.com/presentations/Are-We-There-Yet-Rich-Hickey)

* The [re-frame README](https://github.com/Day8/re-frame)

* [ratom.cljs](https://github.com/reagent-project/reagent/blob/master/src/reagent/ratom.cljs)

* [Turning the database inside out](https://www.youtube.com/watch?v=fU9hR3kiOK0)

* [Simple Made Easy](https://www.infoq.com/presentations/Simple-Made-Easy)



## License



```

Copyright 2015 David Sheldrick 



Licensed under the Apache License, Version 2.0 (the "License");

you may not use this file except in compliance with the License.

You may obtain a copy of the License at



    http://www.apache.org/licenses/LICENSE-2.0



Unless required by applicable law or agreed to in writing, software

distributed under the License is distributed on an "AS IS" BASIS,

WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

See the License for the specific language governing permissions and

limitations under the License.

```