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Reactive JavaScript Objects and Primitives
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oxjs

OxJS is a working in progress library written in TS that enable encapsulated reactivity, distantly inspired by VueJS reactivity system.
The library is compiled into UMD format and uses ES6 Proxies.

$ npm i -S oxjs

 

oxjs bases

ox.observable<T extends object>(obj: T): T

This method takes an object or an array and transform it into an observable, so its fields can be used inside an evaluator to be observed (more on evaluators later):

const { ox } = require('oxjs');

const $observable = ox.observable({ a: 5 });

// or

const obj = { a: 5 };
const $observable = ox.observable(obj);

In the latter case, be sure to apply changes on $observable from this point on or observers won't be notified:

obj.a = newValue; // WRONG

$observable.a = newValue; // NICE

ox.observer<T extends Evaluator>(evaluator: T): ReturnType<T>

This method takes a function, called evaluator, and uses it to produce an observer.
Inside the evaluator, observables' fields will be used, and a value should be retured as the result of the observation process.

const { ox } = require('oxjs');

const $observable = ox.observable([1, 2, 3]);

const sumObserver = ox.observer(function evaluator() {
    // take values from the observable
    const _0 = $observable[0];
    const _1 = $observable[1];
    const _2 = $observable[2];

    // return a result
    return _0 + _1 + _2;
});

The sumObserver observer is called reactive primitive because it will act as a number. In particular its value will be always the sum of the first three fields of the $observable array, also when one of them will change.
That is because those fileds are accessed into the evaluator, so each time one of them changes, the evaluator will be called updating the sumObserver value:

console.log(`${sumObserver}`); // 6

// update the $observable
$observable[0] = 5;

console.log(`${sumObserver}`); // 10

reactive primitives

OxJS let you create special reactive objects that act like a primitive:

const { ox } = require('oxjs');

// it creates two observable sources from two object literals
const $source1 = ox.observable({
    years: 32,
});

const $source2 = ox.observable({
    name: 'Mario',
});

// it creates an observer that will behave as a string
const stringObserver = ox.observer(() => `My name is ${$source2.name} and I'm ${$source1.years} years old`);

// WARNING
typeof stringObserver; // object

// initial evaluation
// interpolation is used because 'stringObserver' is not a real string primitive, it behaves like a String object
// so you need to use interpolation, or to call methods like valueOf(), toString()
console.log(`${stringObserver}`); // My name is Mario and I'm 32 years old

// we change the stored 'years' inside $source1
$source1.years = 28;

// the 'stringObserver' is updated
console.log(`${stringObserver}`); // My name is Mario and I'm 28 years old

// we change the stored 'name' inside $source2
$source2.name = 'Luigi';

// the 'stringObserver' is updated
console.log(`${stringObserver}`); // My name is Luigi and I'm 28 years old

// because 'stringObserver' behaves like a String object, you can use it
// almost everywhere a string is expected and you have access to all of String.prototype methods
stringObserver + "!!!"; // My name is Luigi and I'm 28 years old!!!
stringObserver.toUpperCase(); // MY NAME IS LUIGI AND I'M 28 YEARS OLD!!!

// WARNING HERE: 'stringObserver' is a String object and objects are truthy values
if(stringObserver) { // the condition is always true
// you have to extract its value implicitly or explicitly
if(stringObserver != "") { // coercion :3
if(stringObserver.toString()) {


// same for number and boolean observers
const numberObserver = ox.observer(() => $source1.years * 10);
const booleanObserver = ox.observer(() => $source1.years < 100);

// WARNING
typeof numberObserver; // object
typeof booleanObserver; // object

console.log(`${numberObserver}`); // 280
console.log(`${booleanObserver}`); // true

// we change the stored 'years' inside $source1
$source1.years = 100;

console.log(`${numberObserver}`); // 1000
console.log(`${booleanObserver}`); // false

numberObserver.toExponential(); // 1.00e+3

// WARNING HERE: 'booleanObserver' is a Boolean object and objects are truthy values
booleanObserver && true; // true
// you have to extract its value
booleanObserver.valueOf() && true; // false

// WARNING HERE: 'numberObserver' is a Number object and objects are truthy values
if(numberObserver) { // the condition is always true
// you have to extract its value implicitly or explicitly
if(numberObserver != 0) { // coercion, again :)
if(numberObserver.valueOf()) {

reactive objects

Obviously we are not limited to primitives:

const { ox } = require('oxjs');

// it creates two observable sources from two object literals
const $source1 = ox.observable({
    years: 32,
});

const $source2 = ox.observable({
    name: 'Mario',
});

// it creates a reactive object
const reactiveObject = ox.observer(() => {
    const years = $source1.years;
    const name = $source2.name;
    return {
        years,
        identity: {
            name
        }
    }
});


// initial evaluation
console.log(reactiveObject); // { years: 32, identity: { name: 'Mario' } }

// we change the stored 'years' inside $source1
$source1.years = 28;

// the 'reactiveObject' is updated
console.log(reactiveObject); // { years: 28, identity: { name: 'Mario' } }

// we change the stored 'name' inside $source2
$source2.name = 'Luigi';

// the 'reactiveObject' is updated
console.log(reactiveObject); // { years: 28, identity: { name: 'Luigi' } }

mixed observers

You can mix primitives and objects observers, if you ever find a valid reason to do it:

const { ox } = require('oxjs');

// it creates two observable sources from two object literals
const $source1 = ox.observable({
    years: 32,
});

const $source2 = ox.observable({
    name: 'Mario',
});

const reactiveMess = ox.observer(() => {
    const years = $source1.years;
    const name = $source2.name;

    if (years < 40) {
        return `${years} years aren't enough`;
    } else {
        return {
            years,
            identity: {
                name
            }
        }
    }
});

// initial evaluation
console.log(reactiveMess.valueOf()); // "32 years aren't enough"

// update years
$source1.years = 50;

console.log(reactiveMess.valueOf()); // { years: 50, identity: { name: 'Mario' } }

nested observables props

Observables could have nested props:

const { ox } = require('oxjs');

// it creates an observable source from an object literal with nested properties
const $source = ox.observable({ nested: { value1: 0, value2: 0 } });

// the observer will have three reactiver props
const observer = ox.observer(() => ({
    doubleValue1: $source.nested.value1 * 2,
    value2MinusOne: $source.nested.value2 - 1,
    nested: $source.nested,
}));

// see how encapsulated reactivity works
setInterval(() => {
    $source.nested.value1++;
    $source.nested.value2--;

    console.log("observer.doubleValue: ", observer.doubleValue1);
    console.log("observer.valueMinusOne: ", observer.value2MinusOne);
    console.log("observer.nested: ", observer.nested);
}, 1000);

// after three seconds the '$source.nested' parent reference will be changed
// but also nested observables will update accordingly
setTimeout(() => {
    $source.nested = { value1: 100, value2: 200 };
}, 3000);

reactive arrays

OxJS is pretty good with arrays as well:

const { ox } = require("oxjs");

const $source = ox.observable([1, 2, 3]);

const sum = ox.observer(() => $source.reduce((a, v) => {
    return a + v;
}, 0));

console.log(`reduce result is: ${sum}`); // reduce result is: 6

$source[3] = 4;

console.log(`reduce result is: ${sum}`); // reduce result is: 10

$source.push(10)

console.log(`reduce result is: ${sum}`); // reduce result is: 20

$source.shift()

console.log(`reduce result is: ${sum}`); // reduce result is: 19

observable observers

Observers can be used as observables, increasing the power in your hands.

Example with objects:

const {ox} = require("oxjs");

const $source = ox.observable({foo: 42}); 

// { foo: 84 }
const $doubleSource = ox.observable(ox.observer(() => ({foo: $source.foo * 2})));

// 83
const doubledFooMinusOne = ox.observer(() => $doubleSource.foo - 1);

// "doubledFooMinusOne is 83"
console.log(`doubledFooMinusOne is ${doubledFooMinusOne}`);

$source.foo = 10; // $doubleSource: { foo: 20 }

// "doubledFooMinusOne is 19"
console.log(`doubledFooMinusOne is ${doubledFooMinusOne}`);

Here $doubleSource is both an observer, because it does observe $source.foo doubling its value as result, and an observable, used by another observer: doubledFooMinusOne.  

Example with arrays:

const { ox } = require("oxjs");

const $source = ox.observable([1, 2, 3]);

// [2, 4, 6]
const $doubleMappedSource = ox.observable(ox.observer(() => $source.map(x => x * 2)));

// 12
const sum = ox.observer(() => $doubleMappedSource.reduce((a, b) => a + b, 0));
// 3
const length = ox.observer(() => $doubleMappedSource.length);

// 12 - 3
console.log(`${sum} - ${length}`);

$source.push(4); // $source: [1, 2, 3, 4], $doubleMappedSource: [2, 4, 6, 8]

// 20 - 4
console.log(`${sum} - ${length}`);

Here $doubleMappedSource is both an observer, because it does observe $source doubling its values as result, and an observable, used by both sum and length observers.

observerByProps

The observer method is very powerful, because let you return an observable of any kind. But when it comes to create a reactive object, each time an observable source on which it depends changes, the whole observer is recreated from scratch.
This could constitute performance problems when heavy reactive objects are needed.
Thankfully OxJS provides an API to let you specify a separate observer for each reactive property:

const { ox } = require('oxjs');

// it creates an observable source from an object literal with nested properties
const $source = ox.observable({ nested: { value1: 0, value2: 0 } });

// the observer will have three reactive props
const observer = ox.observerByProps([
    {
        key: 'doubleValue1',
        evaluator() {
            return $source.nested.value1 * 2;
        }
    },
    {
        key: 'value2MinusOne',
        evaluator() {
            return $source.nested.value2 - 1;
        }
    },
    {
        key: 'nested',
        evaluator() {
            return $source.nested;
        }
    }
]);

// see how encapsulated reactivity works
setInterval(() => {
    $source.nested.value1++;
    $source.nested.value2--;

    console.log("observer.doubleValue: ", observer.doubleValue1);
    console.log("observer.valueMinusOne: ", observer.value2MinusOne);
    console.log("observer.nested: ", observer.nested);
}, 1000);

// after three seconds the '$source.nested' parent reference will be changed
// but also nested observables will update accordingly
setTimeout(() => {
    $source.nested = { value1: 100, value2: 200 };
}, 3000);

Currenlty nested props into the observer are not supported. You cannot use Symbols as keys.

tips for TS devs

OxJS is written in TS and it's able to mantain types for observables and is able to extract types from the array of key-executor pair for observers created with observerByProps.
For the latter though TS needs a little help.

observable

const $source1 = ox.observable({
    years: 32,
});

// typeof $source1 is { years: number }

observer created with observerByProps

You have to pass an array as narrow as possible (from a type point of view) to correctly exctract type info.

const observer = ox.observerByProps([
    {
        key: 'doubleValue',
        evaluator() {
            return $source1.years * 2;
        }
    },
] as const); // <- see here

// typeof observer is { doubleValue: number }

observer created with observer

Observers created with observe deserve a separate discussion.
If a reactive object is generated, TS will infer the correct type:

const observer = ox.observer(() => ({
    doubleValue: $source1.years * 2,
}));

// typeof observer is { doubleValue: number }

If a reactive primitive is generated, TS will infer the primitive type:

const observer = ox.observer(() => $source1.years * 2));

// typeof observer is number, not Number

tests

Incoming...

issues

Creating reactive primitives was a mess for me, for Typescript and for ES6 proxies. Have you ever seen a proxy with a dynamic target?
So if something does explode, please be patient and open a polite issue.

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