The Observer Utility

Transparent reactivity with 100% language coverage. Made with :heart: and ES6 Proxies.

Motivation

Popular frontend frameworks - like Angular, React and Vue - use a reactivity system to automatically update the view when the state changes. This is necessary for creating modern web apps and staying sane at the same time.

The Observer Utililty is a similar reactivity system, with a modern twist. It uses ES6 Proxies to achieve true transparency and a 100% language coverage. Ideally you would like to manage your state with plain JS code and expect the view to update where needed. In practice some reactivity systems require extra syntax - like React's setState. Others have limits on the language features, which they can react on - like dynamic properties or the delete keyword. These are small nuisances, but they lead to long hours lost among special docs and related issues.

The Observer Utility aims to eradicate these edge cases. It comes with a tiny learning curve and with a promise that you won't have to dig up hidden docs and issues later. Give it a try, things will just work.

Bindings

This is a framework independent library, which powers the reactivity system behind other state management solutions. These are the currently available bindings.

• React Easy State is a state management solution for React with a minimal learning curve.
• preact-ns-observer provides a simple @observable decorator that makes Preact components reactive.

Installation

$ npm install @nx-js/observer-util

Usage

The two building blocks of reactivity are observables and reactions. Observable objects represent the state and reactions are functions, that react to state changes. In case of transparent reactivity, these reactions are called automatically on relevant state changes.

Observables

Observables are transparent Proxies, which can be created with the observable function. From the outside they behave exactly like plain JS objects.

1import { observable } from '@nx-js/observer-util';
2
3const counter = observable({ num: 0 });
4
5// observables behave like plain JS objects
6counter.num = 12;

Reactions

Reactions are functions, which use observables. They can be created with the observe function and they are automatically executed whenever the observables - used by them - change.

Vanilla JavaScript

1import { observable, observe } from '@nx-js/observer-util';
2
3const counter = observable({ num: 0 });
4const countLogger = observe(() => console.log(counter.num));
5
6// this calls countLogger and logs 1
7counter.num++;

React Component

1import { store, view } from 'react-easy-state';
2
3// this is an observable store
4const counter = store({
5  num: 0,
6  up() {
7    this.num++;
8  }
9});
10
11// this is a reactive component, which re-renders whenever counter.num changes
12const UserComp = view(() => <div onClick={counter.up}>{counter.num}</div>);

Preact Component

1import { observer } from "preact-nx-observer";
2
3let store = observable({ title: "This is foo's data"});
4
5@observer // Component will now re-render whenever store.title changes.
6class Foo extends Component {
7  render() {
8    return <h1>{store.title}</h1>
9  }
10}

More examples

1import { observable, observe } from '@nx-js/observer-util';
2
3const profile = observable();
4observe(() => console.log(profile.name));
5
6// logs 'Bob'
7profile.name = 'Bob';

1import { observable, observe } from '@nx-js/observer-util';
2
3const person = observable({
4  name: {
5    first: 'John',
6    last: 'Smith'
7  },
8  age: 22
9});
10
11observe(() => console.log(`${person.name.first} ${person.name.last}`));
12
13// logs 'Bob Smith'
14person.name.first = 'Bob';

1import { observable, observe } from '@nx-js/observer-util';
2
3const person = observable({
4  firstName: 'Bob',
5  lastName: 'Smith',
6  get name() {
7    return `${this.firstName} ${this.lastName}`;
8  }
9});
10
11observe(() => console.log(person.name));
12
13// logs 'Ann Smith'
14person.firstName = 'Ann';

1import { observable, observe } from '@nx-js/observer-util';
2
3const person = observable({
4  gender: 'male',
5  name: 'Potato'
6});
7
8observe(() => {
9  if (person.gender === 'male') {
10    console.log(`Mr. ${person.name}`);
11  } else {
12    console.log(`Ms. ${person.name}`);
13  }
14});
15
16// logs 'Ms. Potato'
17person.gender = 'female';

1import { observable, observe } from '@nx-js/observer-util';
2
3const users = observable([]);
4
5observe(() => console.log(users.join(', ')));
6
7// logs 'Bob'
8users.push('Bob');
9
10// logs 'Bob, John'
11users.push('John');
12
13// logs 'Bob'
14users.pop();

1import { observable, observe } from '@nx-js/observer-util';
2
3const people = observable(new Map());
4
5observe(() => {
6  for (let [name, age] of people) {
7    console.log(`${name}, ${age}`);
8  }
9});
10
11// logs 'Bob, 22'
12people.set('Bob', 22);
13
14// logs 'Bob, 22' and 'John, 35'
15people.set('John', 35);

1import { observable, observe } from '@nx-js/observer-util';
2
3const defaultUser = observable({
4  name: 'Unknown',
5  job: 'developer'
6});
7const user = observable(Object.create(defaultUser));
8
9// logs 'Unknown is a developer'
10observe(() => console.log(`${user.name} is a ${user.job}`));
11
12// logs 'Bob is a developer'
13user.name = 'Bob';
14
15// logs 'Bob is a stylist'
16user.job = 'stylist';
17
18// logs 'Unknown is a stylist'
19delete user.name;

Reaction scheduling

Reactions are scheduled to run whenever the relevant observable state changes. The default scheduler runs the reactions synchronously, but custom schedulers can be passed to change this behavior. Schedulers are usually functions which receive the scheduled reaction as argument.

1import { observable, observe } from '@nx-js/observer-util';
2
3// this scheduler delays reactions by 1 second
4const scheduler = reaction => setTimeout(reaction, 1000);
5
6const person = observable({ name: 'Josh' });
7observe(() => console.log(person.name), { scheduler });
8
9// this logs 'Barbie' after a one second delay
10person.name = 'Barbie';

Alternatively schedulers can be objects with an add and delete method. Check out the below examples for more.

More examples

1import { observe } from '@nx-js/observer-util';
2
3class ReactiveComp extends BaseComp {
4  constructor() {
5    // ...
6    this.render = observe(this.render, {
7      scheduler: () => this.setState()
8    });
9  }
10}

1import { observable, observe } from '@nx-js/observer-util';
2
3const reactions = new Set();
4const person = observable({ name: 'Josh' });
5observe(() => console.log(person), { scheduler: reactions });
6
7// this throttles reactions to run with a minimal 1 second interval
8setInterval(() => {
9  reactions.forEach(reaction => reaction());
10}, 1000);
11
12// these will cause { name: 'Barbie', age: 30 } to be logged once
13person.name = 'Barbie';
14person.age = 87;

1import { observable, observe } from '@nx-js/observer-util';
2import { Queue, priorities } from '@nx-js/queue-util';
3
4const scheduler = new Queue(priorities.LOW);
5const person = observable({ name: 'Josh' });
6observe(() => console.log(person), { scheduler });
7
8// these will cause { name: 'Barbie', age: 30 } to be logged once
9// when everything is idle and there is free time to do it
10person.name = 'Barbie';
11person.age = 87;

API

Proxy = observable(object)

Creates and returns a proxied observable object, which behaves just like the originally passed object. The original object is not modified.

• If no argument is provided, it returns an empty observable object.
• If an object is passed as argument, it wraps the passed object in an observable.
• If an observable object is passed, it returns the passed observable object.

boolean = isObservable(object)

Returns true if the passed object is an observable, returns false otherwise.

reaction = observe(function, config)

Wraps the passed function with a reaction, which behaves just like the original function. The reaction is automatically scheduled to run whenever an observable - used by it - changes. The original function is not modified.

observe also accepts an optional config object with the following options.

• lazy: A boolean, which controls if the reaction is executed when it is created or not. If it is true, the reaction has to be called once manually to trigger the reactivity process. Defaults to false.

• scheduler: A function, which is called with the reaction when it is scheduled to run. It can also be an object with an add and delete method - which schedule and unschedule reactions. The default scheduler runs the reaction synchronously on observable mutations. You can learn more about reaction scheduling in the related docs section.

• debugger: An optional function. It is called with contextual metadata object on basic operations - like set, get, delete, etc. The metadata object can be used to determine why the operation wired or scheduled the reaction and it always has enough data to reverse the operation. The debugger is always called before the scheduler.

unobserve(reaction)

Unobserves the passed reaction. Unobserved reactions won't be automatically run anymore.

1import { observable, observe, unobserve } from '@nx-js/observer-util';
2
3const counter = observable({ num: 0 });
4const logger = observe(() => console.log(counter.num));
5
6// after this the logger won't be automatically called on counter.num changes
7unobserve(logger);

obj = raw(observable)

Original objects are never modified, but transparently wrapped by observable proxies. raw can access the original non-reactive object. Modifying and accessing properties on the raw object doesn't trigger reactions.

Using raw at property access

1import { observable, observe, raw } from '@nx-js/observer-util';
2
3const person = observable();
4const logger = observe(() => console.log(person.name));
5
6// this logs 'Bob'
7person.name = 'Bob';
8
9// `name` is used from the raw non-reactive object, this won't log anything
10raw(person).name = 'John';

Using raw at property mutation

1import { observable, observe, raw } from '@nx-js/observer-util';
2
3const person = observable({ age: 20 });
4observe(() => console.log(`${person.name}: ${raw(person).age}`));
5
6// this logs 'Bob: 20'
7person.name = 'Bob';
8
9// `age` is used from the raw non-reactive object, this won't log anything
10person.age = 33;

Platform support

• Node: 6.5 and above
• Chrome: 49 and above
• Firefox: 38 and above
• Safari: 10 and above
• Edge: 12 and above
• Opera: 36 and above
• IE is not supported

Alternative builds

This library detects if you use ES6 or commonJS modules and serve the right format to you. The exposed bundles are transpiled to ES5 to support common tools - like UglifyJS minifying. If you would like a finer control over the provided build, you can specify them in your imports.

• @nx-js/observer-util/dist/es.es6.js exposes an ES6 build with ES6 modules.
• @nx-js/observer-util/dist/es.es5.js exposes an ES5 build with ES6 modules.
• @nx-js/observer-util/dist/cjs.es6.js exposes an ES6 build with commonJS modules.
• @nx-js/observer-util/dist/cjs.es5.js exposes an ES5 build with commonJS modules.

If you use a bundler, set up an alias for @nx-js/observer-util to point to your desired build. You can learn how to do it with webpack here and with rollup here.

Contributing

Contributions are always welcomed! Just send a PR for fixes and doc updates and open issues for new features beforehand. Make sure that the tests and the linter pass and that the coverage remains high. Thanks!