JavaScript data structures with immutable state events.

Install

npm install pek

Then:

const pek = require('pek');

Quick Start

To get started, create a data model for your application using the same data types as you would with JSON (String, Number, Boolean, Object, Array, and null):

const APP_STATE = {
  name: 'Todo List',
  lists: [
    {name: 'Shopping', items: ['Milk', 'Bananas']},
  ]
};

Next, create a Pēk model by passing this data model to pek():

const model = pek(APP_STATE); // ⇨ { name: 'Todo List', lists: [ { name: 'Shopping', items: [Object] } ] }

That's pretty much all there is to it. Your Pēk model looks and feels just like the original:

model.lists[0].name = 'Zoo Supplies';
model.lists[0].items.push('Monkeys');

model.lists[0]; // ⇨ { name: 'Zoo Supplies', items: [ 'Milk', 'Bananas', 'Monkeys' ] }

... with one important difference - you can subscribe to state changes:

const unsubscribe = model.__.on(state => console.log(state));

model.name = 'Pek Example';

Anytime your Pēk model changes, all listeners are notified. Moreover, the state listeners receive is immutable:

model.__.on(state => {
  state.name = 'Nopity nope nope';
  state.name; // ⇨ 'Pek Example 2'
});

model.name = '\Pek Example 2';

In non-strict mode, changing the state will fail silently, as above. In strict mode, changing the state will throw an exception:

model.__.on(state => {
  'use strict';
  try {
    state.name = 'Nopity nope nope';
  } catch (err) {
    console.log(err.message);
  }
});

model.name = '\Pek Example 3';

⇒ Cannot assign to read only property 'name' of object '[object Object]'

API

pek(initialState)

Creates a new Pēk model

• initialState - Object or Array holding your initial model state
• Returns a Pēk model (a Proxy-wrapped version of initialState)

E.g.

const model = pek({a: 'hello', b: ['world']}); // ⇨ { a: 'hello', b: [ 'world' ] }

model. ... __.on(callback)

Listen for changes to model state.

• callback - Function to call any time the target object or any of it's subordinate objects change state. This function takes the following arguments:
  • state - An immutable copy of the object state. Attempting to modify
• Returns unsubscriber Function.

const unsubscribe = model.__.on(immutableState => console.log(immutableState));

model.a = 'Hello';

⇒ { a: 'Hello', b: [ 'world' ] }

To unsubscribe, call the returned unsubscriber Function:

unsubscribe();

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