statez
v2.0.0
Published
Simple client-side state manager with events, synchronization, and local storage
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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:
triggers local events where the
details
object has.property
set to'counter'
,.oldValue
set to0
, and.value
set to1000
updates
counter
in localStorage to change the value from0
to1000
. This triggers alocalStorage
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.