Shared multi-paradigm application state and action manager.

It will help you organize the global state of your application, the local state of a separate module, or combine several modules that differ in architecture. It can also work in conjunction with other state managers.

LensJs implement the concept of a functional programming, where the data structure has the form of a directed graph (from the root to the leaves). Each node is an object model that is able to extend the basic prototype with methods and fields. LensJs is base technology for implimentation to any frameworks like ReactJs, Angular, Vue e.t.c.

• Wiki - documentation
• react-lens - ReactJS implementation
• Git (Github) push mirror

• Git: git clone https://git.dev-store.xyz/Clu/lens-js.git
• Npm: npm i @vovikilelik/lens-js

We believe that the structure and organization of the application state should be clear. You don't need to know the entire organization of the state to understand how it functions.

You don't need to write a lot of code to create a simple object. It doesn't take much to figure out how to write a simple object.

LensJs provides both ways to extends like OOP and functional approach. We also take care of the possibility of both scaling.

We think performance is important too (but that's not for sure).

We believe that LensJs can be used in conjunction with other state managers.

• Asynchronous change assambly
• Concurrency
• Catching changies
• Data transform on demand
• Both scalability (out/up)
• Object-oriented and functional approach
• Encapsulation
• Typings with TypeScript

One of the main ideas of lens-js is to create a basic mechanism that could form the basis of shells for other frameworks: ReactJS, Angular, Vue, etc. This would allow many developers to better understand processes on different frameworks and depend less on a particular stack. And also, it would allow achieving good code portability between projects on different frameworks.

|-----------| |-----------| |--------------|
|  ReactJS  | |  Angular  | |  Vue е.т.с.  |
|-----------| |-----------| |--------------|
[react-lens ] [angular-lens] ...
      |             |              |
|------------------------------------------|
|                 lens-js                  |
|------------------------------------------|

See react-lens for ReactJS implementation.

const store = createStore(0);

const Counter: react.FC = () => {
  const [value, setValue] = useLens(store);
  return <button onClick={() => setValue(value + 1)}>{value}<button>;
}

lens-js can be used as a standalone status manager, or as part of a library. It is suitable for use in Web Components or Node Modules.

<script type="module">
  import { createStore } from './path_to_module/index.js';

  const store = createStore({ /* App data */ });
  ...
</script>

import { createStore } from '@vovikilelik/lens-js';

export const store = createStore({ /* App data */ });
...

There are two main approaches to extending the state model: functional, provided by the Store class, and Object-oriented.

The Store class provides a functional approach to creating state. You can add new properties to the model using the extends() method. For convenience, we recommend using the createStore() utility.

export const store = createStore({ /* default data */ })
  .extends({ message: 'Hello' })
  .extends(node => {
    sayHello: (name) => alert(node.hello + ' ' + name)
  });

console.log(store.sayHello('Mike'));  // Hello Mike

The state model has a lazy tree structure. This means that child models will be created only after accessing them via the go() method. However, you can create a model in advance and embed it in another one. In this case, there will be no need to access the go() method, but to access it as a simple field.

The extends() method takes an argument of two types: a simple object and a function that returns an addition to the state prototype. The fields of a simple object will be converted to state properties.

export const message = createStore('Hello World!');

export const store = createStore({})
  .extends({ message });

console.log(store.message.get());  // Hello World!

At the same time, we can always use the go() method as a universal way to access nested models.

store.message === store.go('message')  // true

You can always create and share class-based models. Your classes must be derived from Lens or one of its child classes, like Store

class HelloStore extends Store {
  sayHello(name) => this.go('message').get() + ' ' + name;
}

export const store = createStore({ message: 'Hello' }, HelloStore);
store.sayHello('Tom');  // Hello Tom

Accordingly, such models can be created with a regular constructor. The createStore() utility does about the same thing.

let state = {};

export const store = new HelloStore(
  () => state,  // getter
  value => state = value  // setter
);

In such models, access to nested models can only be obtained through the go() method, unless you yourself have defined such a thing in the class.

However, no one forbids combining both approaches to determining the state. This way you will get the benefits of both approaches.

class Car extends Store {
  move() {}
}

export const car = createStore({}, Car);
export const highway = createStore({})
  .extends({ car });

highway.car.move();

The go() method is a universal way of passing nested nodes. The get() method returns the value stored in the state. Each node will have its own value. Sometimes it doesn't make sense to call get() if the node is converted to a string.

const store = createStore({ one: { two: 'Hi!' } });

const one = store.go('one');  // Like store.one
const two = one.go('two');  // Like one.two

two.get()  // Hi!

You can also create models based on your own prototypes

class Cat extends Store {
  mew() {}
}

const store = createStore({ foo: {} });

const fooIsCat = store.go('foo', Cat);
fooIsCat.mew();

This method is only available when using the extends method or the OOP approach. There is a universal way to get nested nodes - this is the go() method.

const store = createStore({}).extends({ field: 'Hello!' });

console.log(store.field.get())  // Hello!
console.log(store.go('field').get())  // Hello!

Use the view() to access the model data immediately.

const store = createStore({}).view({ count: 0, nested: { foo: 'Hello!' } });

store.count++;  // 1
store.nested.foo;  // Hello!

class MyStore extends Store {
  get field() {
    this.go('field');
  }
}

const store = createStore({ field: 'Hello!' }, MyStore);

console.log(store.field.get())  // Hello!
console.log(store.go('field').get())  // Hello!

The set() method is a universal way to set a new value to a state. To set a new value to a nested node, you first need to get it using the go() method

const store = createStore({ fruit: { name: 'Apple' } });

const name = store.go('fruit').go('name');  // access to value of fruit
name.set('Orange');  // { fruit: { name: 'Orange' } }

You can pass to the set()' method the mutator function.

const store = createStore(0);

const setter = prev => prev + 1;

store.set(setter);  // 1
store.set(setter);  // 2
store.set(setter);  // 3

Each LensJs node is a generator that will allow you to go through existing fields regardless of the data type.

const store = createStore({ one: '1', two: '2' });

for (const node of store)
  console.log(node.get());

// 1
// 2

Also, there is a list() method that immediately returns an array of nodes.

const store = createStore({ one: '1', two: '2' });

console.log(store.list().map(node => node.get()));  // [ '1', '2' ]

Change events can be caught in three stages: on the way to the changed node, in the node itself and in the subtree, after the changed node.

There are two approaches to creating change handlers: through the on() or subscribe() method. The on() method allows you to set a trigger that will trigger at the desired stage or prevent unnecessary triggers.

const store = createStore({ input: '' });

const input = store.go('input');
input.on(Triggers.object, () => console.log('Input changed'));

input.set('Hello!')  // Input changed

You can miss the trigger indication. Then a soft change tracking strategy will be applied, which is suitable for most cases.

input.on(() => console.log('Input changed'));

You can use multiple on() methods in a row or assign more than one handler to one trigger.

const store = createStore({})
  .on(Triggers.strict, () => { ... }, () => { ... })
  .on(Triggers.path, () => { ... });

The subscribe method installs only one listener and offers a PubSub pattern

const store = createStore({});

const unsubscriber = store.subscribe(() => { ... });

The subscribe method will listen to all changes in the lensJs sub-branch of the graph and call a listener for each such case. To filter changes, you can use the Callbacks utility.

const unsubscriber = store.subscribe(Callbacks.object(() => { ... }));

You can use the createCallback utility to combine a listener with a trigger. The custom trigger, by the way, can be implemented by yourself.

const unsubscriber = store.subscribe(createCallback(Trigger.object, () => { ... }));

You can create universal handlers that depend only on the data structure, and not on a specific node. To do this, you can use the second argument of the callback function to refer to the node where the event occurred.

const universalCallback = (event, node) => { console.log(node.get()) };

const store1 = createStore({});
const store2 = createStore({});

store1.on(universalCallback);  // Correct
store2.on(universalCallback);  // Correct

You can use the transform() method to bidirectionally transform data on the fly.

For example, we need the color value to be stored as a number in the state, and output as HEX.

const store = createStore({ color: 0 });

const asHex = lens.go('color')
  .transform(
    v => `#${v.toString(16)}`,
    v => parseInt(v.substring(1), 16);
  );

asHex.set('#aabbcc');

console.log(store.get());  // { color: 11189196 }

There is a lower-level chain method. You can use it to create more flexible transformations. For example, unidirectional read output will look like this:

const store = createStore('Tom');

const transformedStore = store.chain(current => {
  return new Store(() => 'Hello ' + current, current.setter, current);
});

transformedStore.set('Mike');

transformedStore.get();  // Hello Mike
store.get();  // Mike

Also, there is a utility transform() that somewhat simplifies this process.

const transformedStore = store.chain(transform(v => 'Hello ' + v, v => v));

Each LensJs node is a singleton.

store.go('singleton') === store.go('singleton');  // true

You can export every node as const.

const store = createStore({ form: {}, auth: {} });

export const form = store.go('form');
export const auth = store.go('auth');

In fact, you can not keep one state for the entire application, but split it into separate independent models. This improves scalability and performance. It also simplifies testing.

export const form = createStore({});
export const auth = createStore({});

There are several utilities in the LensJs package that simplify development:

• Callbacks - Filters as cover for callback.
• Triggers - Filters as functions for callback.
• Differ - Trigger construction utility.
• Debounce - Debounce and throttling utility.
• createCallback() - Create cover filter for callback.
• createLens() - Creation of store in OOP style.
• createStore() - Creation of store in functionlan style.
• asArray() - Array.form() mapper for helps of type management.

const debounce = new Debounce(1000);

debounce.run(() => console.log('1'));
debounce.run(() => console.log('2'));
debounce.run(() => console.log('3'));

// Output: '3'

Every run() you can set enother timeout.

debounce.run(() => { ... }, 1234);

As finish you can cancel process.

debounce.run(() => console.log('Hi!'), 1000);
debounce.cancel();

// No output

You can use the Callbacks utility to create asynchronous and deferred state change handlers.

const state = createState({});

const unsubscriber = state.subscribe(Callbacks.debounce(() => { ... }, 1000));

For example, you need to process only the last handler of the Promise type with wait timeout:

const state = createState('');

const asyncCallback = Callbacks.acync(
  (event, node) => fetch('https://example.org/' + node),
  response => console.log(response),
  50
);

const unsubscriber = state.subscribe(asyncCallback);

state.set('one');
state.set('two');

// Output from https://example.org/two response

Triggers can be created using the Differ utility. For example, the following code will respond to any field id change.

const store = createStore({});

store.on(Differ.check('id').changed(), () => { ... })

And yes, so you can update your state on demand.

const state = createState({ id: '', data: [] });

const asyncCallback = Callbacks.async(
  (event, node) => fetch('https://example.org/' + node.go('id')),
  ({ records }, event, node) => node.go('data').set(records)
);

state.on(Differ.check('id').changed(), asyncCallback);
state.go('id').set('1');

// Data will be changed

You can also create your own checks with use() method, if necessary. For example, you can create a trigger that will prevent triggering on the input of elements less than it was in the state of the application.

const checkSum = (current, prev) => current > prev;

state.on(
  Differ.check('id').use(checkSum),
  () => { ... }
);

state.id.set(1);  // Triggered
state.id.set(2);  // Triggered
state.id.set(1);  // Not triggered. Need a value greater than 2

You can create sequential handlers for changes. Each handler can be a regular function or an asynchronous one.

// Create pipe
const pipe = Callbacks.pipe(
  () => console.log(1),
  async () => console.log('fetch') || await fetch('https://'),
  () => console.log(3)
);

// Create lens state and subscribe listener on changies
const lens = createLens('');
lens.subscribe(pipe);

// Trigger
lens.set('Hello!')

// Console output:
// 1
// fetch
// 3

For more documentation see Wiki documentation.