0.0.6 • Public • Published


xt8, pronounced "state", is a small, pluggable pub/sub, proxy based (hence the x) application state manager.


import {create, subscribe} from 'xt8';
const state = create({});
subscribe('hello.world', () => console.log('Hello world!'));
state.hello = {world: 0}; // -> Hello, World!


I want a small easily maintainable state manager. xt8 is 140 lines plus another 160 lines of included plugins for validation.

I want to start easy and I don't want to define actions for setting simple properties. If I write something real complex, I use Redux (you should, too!). But for most cases, Redux is overkill.

Still I want to be able to later migrate to an immutable state, if I think the complexity calls for it. xt8 let's me do this without changing calls to the initial dumb state implementation.


import {create} from 'xt8';

"create" returns an ECMAScript Proxy Object. This mostly just proxies property gets and sets to the underlying plain state object (you may also use classes e.g. with getters and setters instead of a plain object). The only thing it really does is wrap sub-objects in nested Proxies and handles setting deep sub-object (e.g. state.obj = {foo: 'bar'}) so that deep subscriptions and hooks are called (in this example e.g. the subscriptions for 'obj.foo', 'obj', and '*').

Apart of that it handles subscriptions and hooks. These are fascilities that make it easy for you to get notified on any changes (with subscriptions) and implement custom behavior using hooks.


import {create, subscribe, unsubscribe} from 'xt8';

const state = create({});

subscribe(onAny); // Shorthand for: subscribe('*', onAny);
subscribe('a',    onA);
subscribe('a.b', onAB);

state.c = {d: 0}; // triggers onAny (once)
state.a = {};     // triggers onAny & onA
state.a.b = 0;    // triggers all three subscriptions
state.a = {b: 0}; // triggers all three subscriptions

unsubscribe(onAny); // Shorthand for: unsubscribe('*', onAny);
unsubscribe('a',    onA);
unsubscribe('a.b', onAB);

function onAny() {console.log('"*"   triggered');}
function onA(  ) {console.log('"a"   triggered');}
function onAB( ) {console.log('"a.b" triggered');}

Note: Subscriptions are triggered after a delay (in a new stack). Thus if you make many changes to the state in a function, each handler will be called at most once.


In addition to the pub/sub API explained above, xt8 has a "hooks" API that lets you hook into any gets, sets, and deletes on your state. getHooks can return computed values, thus allowing the implementation of immutable state while maintaining the straightforward API. setHooks and delHooks let you validate and even compute any changes to the state.

Registering hooks let's you completely customize xt8's behavior and are thus a kind of plugin API. The hook API is a bit alike request- or page-routing APIs in that you register hooks for given paths (or for the global '*' path). Hooks then get called if their respective path is affected.

All hooks get called like the respective ECMAScript Proxy handler functions with an additional argument in front: the affected path:

import {hookDel, hookGet, hookSet, CONTINUE} from 'xt8';

// shorthand for hookDel('*', ...):
hookDel(                (path, target, prop)        => CONTINUE);
hookGet('one.path',     (path, target, prop)        => CONTINUE);
hookSet('another.path', (path, target, prop, value) => CONTINUE);

path is always the path for which the hook was called - e.g. "one.path" for the get-hook. target is the host object of the affected property. prop is the key of the affected property, e.g. "path" for the get-hook. value is the value passed to a setter.

Hook-handlers MUST return specific values. All hooks MAY return CONTINUE. This signifies, that the call was not handled. This is essential for validators among others that check whether a change is okay, but don't process it to effect any changes. The hook handler will then proceed to call further hooks or enact the proxie's default behavior.

When not returning CONTINUE setHooks and del-hooks MUST return trueish or falseish in order to signify, whether the change was successful. Falseish will raise an exception! If a getHook returns anything but CONTINUE, that return value will be passed to the code that triggered the get.

Shipped Plugins

xt8 ships a couple of plugins for validation:

import {int} from 'xt8';

This enforces that state.count is only ever set to integer values. It is a shorthand call for

import {hookSet, intValidator} from 'xt8';
hookSet('count', intValidator);

You should never need the latter syntax, but if you happen to want o unreegister a validation, then you'll need

import {unhookSet, int, intValidator} from 'xt8';
unhookSet('count', intValidator);

Thus most validators come in pairs and those that generate closures return those for your unregistering.

The following validators are available:

  • mustHave property must exist; setup function registers get-, set-, and del-hooks
  • mustHaveOwn own property must exist; setup function registers get-, set-, and del-hooks
  • addPropOnlyArray properties can be added only to arrays, not objects; set-hook
  • delPropOnlyArray properties can be deleted only from arrays, not objects; del-hook
  • sameType setters cannot change the type (typeof) of the affected property
  • oneOf validate set against enum (value array)
  • int property only accepts intergers in set
  • configureTemplate allows you to define the structure of your state in one call, see demo

The actual validators have the same name as their respective setup-functions with an appended "Validator". You'll also need to use the actual validators instead of setup functions if you for example want to register mustHave only for setters. In this case, getters would just return undefined und deletes would silently delete a non-existing property.

configureTemplate is pretty specific and does a relative lot of things. It provides a very easy way of defining and enforcing the structure and typografy of your state store. It's a good way to get started with a project. It will help you remain consistent while you keep adding stuff to your state and perpetually remind you to clean up previous versions of your state, should they linger somewhere. However, in later phases of your project, you may want to replace this somewhat simple template mechanism with a more elaborate state validation engine of your own design. Please refer to the demo on how to use configureTemplate.

I hope you find xt8 useful.

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