name: State
purpose: Provide reactive state, declarative DOM directives, and the custom component runtime.

globals:
  State: 'Reactive in-memory application state.'
  Hash: 'Reactive JSON values persisted in location.hash.'
  LocalStorage: 'Reactive JSON values persisted in localStorage.'
  NewState: 'NewState(defaults, getter?, setter?) -> reactive object.'

state:
  watch: 'state.__watch(key, callback); key=null watches every write.'
  unwatch: 'state.__unwatch(key, callback).'
  rules:
    - Assign through State, Hash, LocalStorage, component.state, or a NewState object to notify bindings.
    - Hash and LocalStorage values must be JSON-serializable.
    - Do not use __unsafeRefreshState in application code.

directives:
  $text: 'Set textContent. Without a value, evaluates the element text as a template.'
  $html: Set innerHTML.
  $class: 'Set dynamic classes while retaining static classes.'
  $style: 'Set dynamic styles while retaining static styles.'
  $if: Conditionally render a node or template.
  $each: 'Render an iterable; supports as and index.'
  $bind: Two-way bind a form control or component value.
  $onname: 'Register an event handler; for example $onclick.'
  $.path: 'Evaluate once during component initialization and assign its property path.'
  .path: 'Bind an evaluated value to a DOM or component property path.'
  $$if: 'Evaluate its value once, then evaluate the resulting expression. Use schema expressions such as `$$if="item.if"`.'
  $$each: 'Two-stage equivalent of $each when the iterable expression itself is stored as data.'

expression:
  values: [State, Hash, LocalStorage, top-level const data, this, this.parent, event, thisNode]
  rules:
    - 'Define page data with top-level const before DOM parsing, then bind it directly: `$.state.list="users"`.'
    - Use `this` in a component template and `this.parent` from nested component/template content.
    - Use template around $if or $each when the surrounding DOM must remain intact.
    - Use key for large or identity-sensitive $each lists.

component:
  register: 'Component.register(name, setup, template?).'
  instance: 'Every component has this.state; public API is its attributes, state, methods, events, and slots.'
  slots: '`slot="name"` supplies content; `slot-id="name"` receives it in a component template.'
  lifecycle:
    $onload: After initialization.
    $onupdate: After a bound node updates.
    $onunload: Before a bound node is removed.
  rules:
    - Keep required public behavior declarative; do not expose internal DOM as an application contract.
    - A bindable component listens for bind and writes event.detail into its state.

examples:
  bindings: |
    <script>
      const users = [{ id: 'ada', name: 'Ada' }]
    </script>
    <div $text>Hello ${users[0].name}</div>
    <List $.state.list="users"></List>
    <button $onclick="State.dark = !State.dark">Toggle</button>
  component: |
    <script>
      Component.register('Counter', container => {
        container.state.value = 0
        container.addEventListener('bind', event => { container.state.value = event.detail })
      }, Util.makeDom('<button $text="this.state.value" $onclick="this.state.value++"></button>'))
    </script>
    <Counter $bind="State.count"></Counter>

tests:
  - https://apigo.cc/web/state/raw/branch/main/test/all.spec.js