@aofl/store

Centralized state management for aofljs applications

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Readme

@aofl/store

@aofl/store is a built on the same principles as redux and attempts to simplify some of Redux's concepts. It also incorporates ideas from other centralized state management implementations.

Api Documentation


Examples


Installation

npm i -S @aofl/store

Concepts

State

In @aofl/store the state consists of a collection of sub-states. This allows us to add new sub-states at runtime which leads to constructing an efficient state object based on the applications current needs.

The state object must not be mutated directly. In fact, when debug mode is enabled, Object.freeze is called on every property of the state, attempting to mutate the state will throw an error.

State Definition Object (SDO)

A State Definition Object (SDO) is an object that defines the properties of a sub-state. SDOs must define a namespace, state properties and initial values, optionally mutation functions and decorators.

Here's an example of an SDO configured with all the valid options.

import {Sdo, decorate, state, storeInstance} from '@aofl/store';

class AccountsSdo extends Sdo {
  static namespace: 'accounts';

  @state() id = 0;
  @state() username = '';
  @state() firstName = '';
  @state() lastName = '';
  @state() email = '';
  @state() phone = 0;
  @state() createdTimestamp = 0;
  @state() products = [];

  addProduct(product) {
    this.products = [
      ...this.products,
      product
    ];
  }

  @decorate('accounts.createdTimestamp')
  get formattedCreated() {
    return new Date(this.date).toLocaleDateString('en-US');
  }
}

const accountsSdo = new AccountsSdo();
storeInstance.addState(accountsSdo);

export {accountsSdo};
namespace

sub-states are keyed by namespace. Additionally mutations can only be invoked using the namespace and can only modify the sub-state attached to a namespace. The Sdo class abstracts away interacting with the store directly.

// storeInstance.state
{
  accounts: { // namespace
    id: 0,
    username: '',
    ...
  }
}
@state

Properties decorated with @state are added to Store. Furthermore, the initialized values are used to reset store if necessary. These properties are created with specialized getter/setter functions. The getter proxies the values from store.state.{namespace}.property. This means directly committing a change to store will reflect in the sdo instance. The setter function commits the new value to store.

In addition to the state variables, additional methods can be implemented to apply more complex mutations. E.g. inserting into an array or updating nested properties of an object.

@decorate

Decorators are used to derive new information based on the state of the application. E.g. formatting timestamps to formatted date strings or calculating number of pages based on pagination data (limit per page and total results).

@decorate() takes variadic arguments that map to properties in store. Hence, the paths used include namespace. This allows us to observe changes across multiple SDOs. Consider the case where the decorated value should update when user's preferred locale changes. A decorator can observe changes in UserSettingsSdo and update timestamps accordingly in other SDOs.

Decorated properties are memoized based on the arguments passed to @decorate. I.e. the values are computed when accessed and only recomputed when observed values change.

import {userSettingsSdo} from 'user-settings-sdo';

class AccountsSdo extends Sdo {
  static namespace: 'accounts';
  ...
  @state() createdTimestamp = 0;
  ...

  @decorate('accounts.createdTimestamp', `${userSettingsSdo.namespace}.locale`)
  get formattedCreated() {
    return new Date(this.date).toLocaleDateString(userSettingsSdo.locale);
  }
}

addState()

Adds a new Sdo to store.

commit()

To change state commit() can be used. It accepts a namespace and a mutation objects as arguments.

storeInstance.commit('accounts', {
  id: 1
});

subscribe()

You can subscribe to store to receive updates. The subscribe function returns the unsubscribe function.

const unsubscribe = storeInstance.subscribe(() => {
  const state = store.getState();
  view.lastLoginDate = state.accounts.$formattedLastLogin;
});

view.onDestroy(() => {
  unsubscribe();
});

flushState()

Resets the state to the initial state of Sdos.

storeInstance.flushState();

Usage with @aofl/element

@property decorator exported from @aofl/element extends the @property decorator from lit-element and adds 2 new keys to the options mapState and store.

mapState is a string path relative to the provided store's state property. store defaults to storeInstance exported from @aofl/store. It can be replaced with an instance of store or an sdo class.

import {AoflElement, property, customElement} from '@aofl/element';
import template from './template';
import styles from './styles';
import {previewSdo} from '../preview-sdo';

@customElement('example-component)
class ExampleComponent extends AoflElement {
  constructor() {
    super();
  }

  static is = 'example-component';

  @property({mapState: 'count', store: previewSdo})
  count = 0;

  @property({mapState: 'formattedDate', store: previewSdo})
  formattedDate = '';

  incrementCount() {
    previewSdo.increment();
  }

  render() {
    return super.render(template, [styles]);
  }
}

If you find any bugs or have a feature request, please open an issue on github!

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