@alwatr/render-state

@alwatr/render-state

State-based rendering utility for Unidirectional Data Flow architectures.

@alwatr/render-state provides a clean, type-safe utility for mapping application state values to render functions — the missing piece between your state signals and your UI templates.

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Why @alwatr/render-state?

In reactive applications, you often need to render different UI based on the current state of a signal or FSM. Without a utility, this leads to verbose if/else chains or switch statements scattered throughout your rendering code.

renderState gives you a declarative render map — a plain object that maps each state value to a render function, with a _default fallback for unhandled states.

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Installation

bun add @alwatr/render-state
# or
npm i @alwatr/render-state

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Quick Start

import {renderState} from '@alwatr/render-state';

type LoadingState = 'idle' | 'loading' | 'success' | 'error';

const currentState: LoadingState = 'loading';

const result = renderState(currentState, {
  idle: () => '<p>Ready to load</p>',
  loading: () => '<p>Loading...</p>',
  success: () => '<p>Data loaded successfully!</p>',
  error: () => '<p>Something went wrong.</p>',
  _default: 'idle', // Fallback to 'idle' render for unknown states
});

console.log(result); // '<p>Loading...</p>'

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API Reference

renderState<R, T>(state, renderRecord, thisArg?)

Maps a state value to a render function and executes it.

function renderState<R, T extends string>(
  state: T,
  renderRecord: Record<T | '_default', undefined | T | (() => R)>,
  thisArg?: unknown,
): R | undefined;

Parameters:

• state — the current state value (must be a string)
• renderRecord — an object mapping each state to a render function or alias
• thisArg — optional this context for render functions

Render record values:

Value type	Behavior
() => R	Calls the function and returns the result
string	Treats as an alias — looks up that key in the render record
undefined	Falls through to _default

_default key:

• If the current state has no matching render function, _default is used
• _default can be a function (direct fallback) or a string (alias to another state's render)
• If _default is also undefined, logs an error and returns undefined

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Advanced Usage

State Aliasing

Multiple states can share the same render function via string aliases:

type OrderState = 'pending' | 'processing' | 'shipped' | 'delivered' | 'cancelled' | 'refunded';

renderState(currentOrderState, {
  pending: () => renderPendingUI(),
  processing: 'pending', // Alias — uses the 'pending' render function
  shipped: () => renderShippedUI(),
  delivered: () => renderDeliveredUI(),
  cancelled: () => renderCancelledUI(),
  refunded: 'cancelled', // Alias — uses the 'cancelled' render function
  _default: 'pending',
});

With lit-html Templates

renderState pairs naturally with lit-html for reactive UI rendering:

import {renderState} from '@alwatr/render-state';
import {html, render} from 'lit-html';

type FetchState = 'idle' | 'loading' | 'success' | 'error';

function renderApp(state: FetchState, data?: string[]) {
  render(
    renderState(state, {
      idle: () => html`
        <button @click=${fetchData}>Load Data</button>
      `,
      loading: () => html`
        <div class="spinner">Loading...</div>
      `,
      success: () => html`
        <ul>
          ${data?.map(
            (item) => html`
              <li>${item}</li>
            `,
          )}
        </ul>
      `,
      error: () => html`
        <p class="error">
          Failed to load.
          <button @click=${fetchData}>Retry</button>
        </p>
      `,
      _default: 'idle',
    }),
    document.getElementById('app')!,
  );
}

With Signal Subscriptions

import {createStateSignal} from '@alwatr/flux';
import {renderState} from '@alwatr/flux';

type AppState = 'auth' | 'home' | 'settings' | 'loading';

const appStateSignal = createStateSignal<AppState>({
  name: 'app-state',
  initialValue: 'loading',
});

appStateSignal.subscribe((state) => {
  const content = renderState(state, {
    loading: () => renderLoadingScreen(),
    auth: () => renderAuthPage(),
    home: () => renderHomePage(),
    settings: () => renderSettingsPage(),
    _default: 'loading',
  });

  document.getElementById('root')!.innerHTML = content ?? '';
});

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Part of Alwatr Flux

@alwatr/render-state is a utility in the Alwatr Flux architecture — a complete Unidirectional Data Flow system for building scalable Progressive Web Applications.

In the Flux architecture, renderState lives at the boundary between the State Layer and the View Layer. It translates signal values into UI output without any coupling to the state management system itself.

State Layer (@alwatr/signal)
  ↓ signal.subscribe(state => ...)
renderState(state, renderMap)  ← @alwatr/render-state
  ↓
View Layer (HTML / lit-html templates)

// Use @alwatr/flux for the complete architecture
import {renderState, createStateSignal, onAction} from '@alwatr/flux';

// Or use @alwatr/render-state standalone
import {renderState} from '@alwatr/render-state';

→ View the complete Flux documentation

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Contributing

Contributions are welcome! Please read our contribution guidelines before submitting a pull request.

License

MPL-2.0 — see LICENSE.