stateZ

stateZ (state-easy) is a simple client-side state manager. Features:

• simple to use, e.g. myState.x = 1; console.log( myState.x );
• triggers events when a state changes
• synchronizes data across browser tabs and windows on the same domain
• vanilla JavaScript compatible with all frameworks
• fast and lightweight - less than 2KB of code

The stateZ version 2 API differs to version 1. Refer to UPGRADE.md for migration details.

Compatibility

stateZ works in modern browsers which support ES modules.

stateZ comparison

stateZ 2.0 works in a similar way to stateZx:

feature	stateZ	stateZx
code size	2Kb	4.5Kb
storage	localStorage	indexedDB
storage limit	typically 5MB	typically 1GB
data types	stringified values	values, objects, blobs
data lifetime	permanent	permanent
performance	good, but synchronous storage	good with asynchronous storage

stateZ is a good option for web sites with minimal storage requirements. stateZx may be preferable for complex web apps storing large amounts of data.

Installation

Load the module from a CDN:

import { stateZ } from 'https://cdn.jsdelivr.net/npm/statez/dist/statez.js';

If using npm and a bundler, install with:

npm install statez

then import the module locally (path resolution will depend on the bundler):

import { stateZ } from './node_modules/statez/dist/statez.js';

Examples

Create/access a named state store by passing an optional ID and initialization object:

const state = stateZ('myState', { a: 1, b: 2, c: 3 });

Any state object on any page in any tab or window on the same domain which accesses the same "myState" store has access to the same properties. Previously-stored values initialize the properties. If a is not defined, the initialization object sets state.a to 1.

Set and retrieve values:

// set state
state.x = 123;
state.y = 'abc';

// get state
console.log( state.x, state.y ); // 123 abc

// output all properties
for (let p in state) {
  console.log(`${ p }: ${ state[p] }`);
}

// delete state
delete state.x; // or
state.x = undefined;

Get the store name:

console.log( state.stateId ); // myState

Run an event handler when any property changes:

// event handler function
function stateEventHandler(evt) {

  const d = evt.detail;
  console.log(`
    ${ d.property } has changed
    from ${ d.valueOld } to ${ d.value }
    in store ${ d.store.stateId }
    (event type "${ evt.type }")
  `);

}

// handle any state change
state.addEventListener('*', stateEventHandler);

or when an individual property changes:

// handle changes to state.a property
state.addEventListener('a', stateEventHandler);

Example:

state.a = 'one';

/*
both the "a" and "*" events trigger - ouput:
a has changed from 1 to one in store myStore (event type "a")
a has changed from 1 to one in store myStore (event type "*")
*/

state.b = 'two';

/*
the "*" event triggers - ouput:
b has changed from 2 to two in store myStore (event type "*")
*/

API reference

Create/access a named store using the stateZ constructor with optional parameters:

name	type	description
stateId	string	state identifier (stateZ if not defined)
stateDefault	object	initialization object

The stateId can be any string, but do not use space or . characters.

The initialization object can contain any number of key/value pairs, e.g.

const state = stateZ('myState', {
  a: 1,
  b: 'two',
  c: false,
  xArray: [1,2,3],
  yObject: { p1: 'prop1', p2: 'prop2' }
});

stateZ uses previously-stored database values by default. Therefore, state.a is only set to 1 if it's initially undefined (or was stored as 1). Setting a new value triggers events, stores it in localStorage, and synchronizes with other tabs/windows using stateZ on the same domain (which trigger their own events).

.stateId

Returns the state identifier (read-only):

console.log( state.stateId ); // myState

set, get, and delete properties

Set and get any property using a valid name and value:

state.prop1 = 'my first property';

console.log( state.prop1 );     // my first property
console.log( state['prop1'] );  // my first property

Delete a property:

delete state.prop1;
// or: delete state['prop1'];
// or: state.prop1 = undefined;
// or: state['prop1'] = undefined;
console.log( state.prop1 );     // undefined

Delete all properties:

for (let p in state) delete state[p];

Property:

• names can contain letters in any case, numbers, or hyphens - but must start with a letter
• values can be any value which can be serialized using JSON.stringify() - anything except for Symbol and functions. Date() objects are stringified so you may need to re-initialize after calling the stateZ constructor, e.g. state.myDate = new Date( state.myDate );

Values are checked to ensure they've changed before triggering events, storage, and tab/window synchronization. Setting state.a = 1 only has an effect when it's not already 1.

Setting properties to objects or arrays

Setting a property to an object or array will always trigger events, storage, and tab/window synchronization. This occurs because objects are passed by reference. Two objects or arrays are not the same even when their values are identical:

console.log( state.myArray );   // [1,2,3]
state.myArray = [1,2,3];        // triggers event, store, sync

console.log( state.myObject );  // {a:1,b:2}
state.myObject = {a:1,b:2};     // triggers event, store, sync

Setting a child property or array element will not trigger events, storage, and synchronization:

state.myArray.push[4];  // not handled
state.myObject.a = 99;  // not handled
state.myObject.c = 100; // not handled

It may be preferable to update the whole object or create separate stateZ stores with native values rather than use nested arrays and objects.

.set(property, value)

Sets temporary session-like values in the current tab. It does not trigger events, storage, and synchronization:

// set value
state.set('temp', 'temporary value');
console.log(state.temp); // temporary value

// delete value
state.set('temp');
console.log(state.temp); // undefined

State change events

You can trigger event handler functions when any property changes:

// handle any state change
state.addEventListener('*', stateEventHandler);

or when an individual property changes:

// handle changes to state.myProp property
state.addEventListener('myProp', stateEventHandler);

Changes to state.myProp triggers both event handlers (the more specific 'myProp' handler runs first).

The handler function receives a single object containing information about the event. Its .detail property defines an object with the following properties:

property	description
.property	name of the updated property
.value	the new value
.valueOld	the old value
.state	the state object

Example:

// event handler function
function stateEventHandler(evt) {

  const d = evt.detail;
  console.log(`stateId       : ${ d.store.stateId }`);
  console.log(`property name : ${ d.property }`);
  console.log(`new value     : ${ d.value }`);
  console.log(`previous value: ${ d.valueOld }`);

}

A state change also triggers events on other tabs and windows that use stateZ with the same store on the same domain.

Remove event handlers with the .removeEventListener() method:

state.removeEventListener('*', stateEventHandler);
state.removeEventListener('myProp', stateEventHandler);

Event and synchronization lifecycle

You can synchronously change and examine any stateZ object's properties in real time. There are no asynchronous operations.

stateZ records all property changes. A later iteration of the JavaScript event loop triggers events, updates storage, and synchronizes across tabs/windows when the CPU is idle. Consider the following code:

let counter = state.counter;

for (let i = 0; i < 1000; i++) {
  counter++;
  state.counter = counter;
}

The code will not trigger 1,000 event, storage, and synchronization processes. If state.counter is initially stored as 0, the synchronous loop will complete and it's value changes to 1000. The update process runs at some future point which:

1. triggers local events where the details object has .property set to 'counter', .oldValue set to 0, and .value set to 1000

2. updates counter in localStorage to change the value from 0 to 1000. This triggers a localStorage event on all tabs/windows on the same domain using stateZ which triggers identical events.

Intensive state changes do not have a significant impact on performance because stateZ makes background updates when the program is idle. Nothing would run if state.counter = 0; was added after the loop!

Usage policy

You are free to use this as you like but please do not republish it as your own work.

Please consider sponsorship if you use stateZ commercially, require support, or want new features.