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

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 usesES6 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'ssetState. Others have limits on the language features, which they can react on - like dynamic properties or thedelete 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.

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.

$ npm install @nx-js/observer-util

The two building blocks of reactivity areobservables andreactions. 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 are transparent Proxies, which can be created with theobservable function. From the outside they behave exactly like plain JS objects.

import{observable}from'@nx-js/observer-util';constcounter=observable({num:0});// observables behave like plain JS objectscounter.num=12;

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

import{observable,observe}from'@nx-js/observer-util';constcounter=observable({num:0});constcountLogger=observe(()=>console.log(counter.num));// this calls countLogger and logs 1counter.num++;

import{store,view}from'react-easy-state';// this is an observable storeconstcounter=store({num:0,up(){this.num++;}});// this is a reactive component, which re-renders whenever counter.num changesconstUserComp=view(()=><divonClick={counter.up}>{counter.num}</div>);

import{observer}from"preact-nx-observer";letstore=observable({title:"This is foo's data"});@observer// Component will now re-render whenever store.title changes.classFooextendsComponent{render(){return<h1>{store.title}</h1>}}

import{observable,observe}from'@nx-js/observer-util';constprofile=observable();observe(()=>console.log(profile.name));// logs 'Bob'profile.name='Bob';

import{observable,observe}from'@nx-js/observer-util';constperson=observable({name:{first:'John',last:'Smith'},age:22});observe(()=>console.log(`${person.name.first}${person.name.last}`));// logs 'Bob Smith'person.name.first='Bob';

import{observable,observe}from'@nx-js/observer-util';constperson=observable({firstName:'Bob',lastName:'Smith',getname(){return`${this.firstName}${this.lastName}`;}});observe(()=>console.log(person.name));// logs 'Ann Smith'person.firstName='Ann';

import{observable,observe}from'@nx-js/observer-util';constperson=observable({gender:'male',name:'Potato'});observe(()=>{if(person.gender==='male'){console.log(`Mr.${person.name}`);}else{console.log(`Ms.${person.name}`);}});// logs 'Ms. Potato'person.gender='female';

import{observable,observe}from'@nx-js/observer-util';constusers=observable([]);observe(()=>console.log(users.join(', ')));// logs 'Bob'users.push('Bob');// logs 'Bob, John'users.push('John');// logs 'Bob'users.pop();

import{observable,observe}from'@nx-js/observer-util';constpeople=observable(newMap());observe(()=>{for(let[name,age]ofpeople){console.log(`${name},${age}`);}});// logs 'Bob, 22'people.set('Bob',22);// logs 'Bob, 22' and 'John, 35'people.set('John',35);

import{observable,observe}from'@nx-js/observer-util';constdefaultUser=observable({name:'Unknown',job:'developer'});constuser=observable(Object.create(defaultUser));// logs 'Unknown is a developer'observe(()=>console.log(`${user.name} is a${user.job}`));// logs 'Bob is a developer'user.name='Bob';// logs 'Bob is a stylist'user.job='stylist';// logs 'Unknown is a stylist'deleteuser.name;

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.

import{observable,observe}from'@nx-js/observer-util';// this scheduler delays reactions by 1 secondconstscheduler=reaction=>setTimeout(reaction,1000);constperson=observable({name:'Josh'});observe(()=>console.log(person.name),{ scheduler});// this logs 'Barbie' after a one second delayperson.name='Barbie';

Alternatively schedulers can be objects with anadd anddelete method. Check out the below examples for more.

import{observe}from'@nx-js/observer-util';classReactiveCompextendsBaseComp{constructor(){// ...this.render=observe(this.render,{scheduler:()=>this.setState()});}}

import{observable,observe}from'@nx-js/observer-util';constreactions=newSet();constperson=observable({name:'Josh'});observe(()=>console.log(person),{scheduler:reactions});// this throttles reactions to run with a minimal 1 second intervalsetInterval(()=>{reactions.forEach(reaction=>reaction());},1000);// these will cause { name: 'Barbie', age: 30 } to be logged onceperson.name='Barbie';person.age=87;

import{observable,observe}from'@nx-js/observer-util';import{Queue,priorities}from'@nx-js/queue-util';constscheduler=newQueue(priorities.LOW);constperson=observable({name:'Josh'});observe(()=>console.log(person),{ scheduler});// these will cause { name: 'Barbie', age: 30 } to be logged once// when everything is idle and there is free time to do itperson.name='Barbie';person.age=87;

Creates and returns a proxied observable object, which behaves just like the originally passed object. The original object isnot 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.

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

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 isnot 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 anadd anddelete method - which schedule and unschedule reactions. The default scheduler runs the reaction synchronously on observable mutations. You can learn more about reaction scheduling in therelated 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.

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

import{observable,observe,unobserve}from'@nx-js/observer-util';constcounter=observable({num:0});constlogger=observe(()=>console.log(counter.num));// after this the logger won't be automatically called on counter.num changesunobserve(logger);

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.

import{observable,observe,raw}from'@nx-js/observer-util';constperson=observable();constlogger=observe(()=>console.log(person.name));// this logs 'Bob'person.name='Bob';// `name` is used from the raw non-reactive object, this won't log anythingraw(person).name='John';

import{observable,observe,raw}from'@nx-js/observer-util';constperson=observable({age:20});observe(()=>console.log(`${person.name}:${raw(person).age}`));// this logs 'Bob: 20'person.name='Bob';// `age` is used from the raw non-reactive object, this won't log anythingperson.age=33;

• 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

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 webpackhere and with rolluphere.

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 thatthe coverage remains high. Thanks!