@wc-bindable/lit

Lit adapter for the wc-bindable protocol.

Install

npm install @wc-bindable/lit lit

Usage

import { LitElement, html } from "lit";
import { createRef, ref } from "lit/directives/ref.js";
import { WcBindableController } from "@wc-bindable/lit";

class TodoView extends LitElement {
  private todoRef = createRef<HTMLElement>();
  private todo = new WcBindableController<{ items: string[]; count: number }>(
    this,
    () => this.todoRef.value,
    { items: [], count: 0 },
  );

  render() {
    return html`
      <lit-todo ${ref(this.todoRef)}></lit-todo>
      <p>Count: ${this.todo.values.count}</p>
      <ul>
        ${this.todo.values.items.map((i) => html`<li>${i}</li>`)}
      </ul>
    `;
  }
}
customElements.define("todo-view", TodoView);

If the host itself is the bindable element you can pass it directly:

this.controller = new WcBindableController(this, this);

API

new WcBindableController<V>(host, target, initialValues?, options?)

| Parameter | Type | Description | |---|---|---| | host | ReactiveControllerHost | Lit host (typically this inside a LitElement) | | target | HTMLElement \| null \| undefined \| () => HTMLElement \| null \| undefined | The bindable element, or a getter that returns it once it is rendered | | initialValues | Partial<V> | Optional initial values for bindable properties |

| Member | Type | Description | |---|---|---| | values | V | Latest property values; reading from render() is reactive |

• Binds on hostConnected and unbinds on hostDisconnected.
• On every host update the target is re-resolved; if it changed, listeners are rebound to the new element.
• Calls host.requestUpdate() whenever a bindable property changes.
• If the element does not implement wc-bindable — and is not a custom element still waiting for its definition — the controller is a no-op. See Late-defined elements.

Late-defined elements

bind() is called with syncOn: "define" by default, so an element whose custom element definition arrives after this adapter runs — import-map autoloading, a CDN <script type="module">, a code-split route — still binds once the definition lands. Nothing has to re-run, and no re-render is needed.

Before this default, a not-yet-upgraded element was skipped permanently and silently: discovery failed, the adapter returned early, and because the element keeps its identity across upgrade nothing ever noticed. Opt back into that behavior with syncOn: "call".

new WcBindableController(host, () => this.el, { value: "" }, { syncOn: "call" });

See SPEC.md § Deferring Discovery Until Definition.

Specification

The protocol contract this adapter implements lives in SPEC.md; the optional input/command invocation surface and the remote wire format live in SPEC-extensions.md. Runnable conformance vectors are in CONFORMANCE.md.

License

MIT