@tcn/state

@tcn/state

A lightweight, type-safe state management library for TypeScript applications.

Table of Contents

• Installation
• Quick Start
• Core Concepts
• Using Signals
• Using Runners
• React Integration
• API Reference
• Troubleshooting

Installation

npm install @tcn/state
# or
yarn add @tcn/state
# or
pnpm add @tcn/state

Quick Start

Basic Counter Example

// CounterPresenter.ts
class CounterPresenter {
  private _countSignal: Signal<number>;

  get countBroadcast() {
    return this._countSignal.broadcast;
  }

  constructor() {
    this._countSignal = new Signal<number>(0);
  }

  increment() {
    this._countSignal.transform(count => count + 1);
  }

  decrement() {
    this._countSignal.transform(count => count - 1);
  }

  dispose() {
    this._countSignal.dispose();
  }
}

// Counter.tsx
function Counter({ presenter }: { presenter: CounterPresenter }) {
  const count = useSignalValue(presenter.countBroadcast);

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={() => presenter.increment()}>Increment</button>
      <button onClick={() => presenter.decrement()}>Decrement</button>
    </div>
  );
}

Core Concepts

The library provides two main classes for state management:

• Signal: Base class for reactive state management

  • Manages a single value of type T
  • Notifies subscribers when the value changes
  • Provides memory-efficient updates through transform

• Runner: Extends Signal for handling async operations

  • Manages async operation state (INITIAL, PENDING, SUCCESS, ERROR)
  • Provides progress tracking and error handling
  • Supports retry and reset operations

Using Signals

Signals are designed to be encapsulated within classes, providing controlled access to state through readonly interfaces.

Basic Usage

class TodoListPresenter {
  private _todosSignal: Signal<Todo[]>;
  private _completedTodosSignal: Signal<number>;

  get todosBroadcast() {
    return this._todosSignal.broadcast;
  }

  get completedCountBroadcast() {
    return this._completedTodosSignal.broadcast;
  }

  constructor() {
    this._todosSignal = new Signal<Todo[]>([]);
    this._completedTodosSignal = new Signal<number>(0);

    this._todosSignal.subscribe(todos => {
      this._completedTodosSignal.set(
        todos.filter(todo => todo.completed).length
      );
    });
  }

  dispose() {
    this._todosSignal.dispose();
    this._completedTodosSignal.dispose();
  }
}

Using Runners

Runners provide a powerful way to manage asynchronous operations with built-in state management.

Status Types

• INITIAL: Default state, no operation running
• PENDING: Operation in progress, progress can be updated
• SUCCESS: Operation completed successfully
• ERROR: Operation failed, contains error information

Basic Usage

class DataServicePresenter {
  private _dataRunner: Runner<Data>;

  get dataBroadcast() {
    return this._dataRunner.broadcast;
  }

  constructor() {
    this._dataRunner = new Runner<Data>(null);
  }

  async fetchData() {
    await this._dataRunner.execute(async () => {
      const response = await fetch('/api/data');
      return await response.json();
    });
  }

  dispose() {
    this._dataRunner.dispose();
  }
}

React Integration

Presenter Patterns

• Root Presenter Pattern (Recommended)

  class AppPresenter {
    readonly userPresenter: UserPresenter;
    
    constructor() {
      this.userPresenter = new UserPresenter();
    }
    
    dispose() {
      this.userPresenter.dispose();
    }
  }
  

• Local State Pattern (For isolated components)

  function MyComponent() {
    const [presenter] = useState(() => new MyPresenter());
    
    useEffect(() => {
      return () => presenter.dispose();
    }, [presenter]);
    
    return <div>...</div>;
  }
  

React Hooks

• useSignalValue<T>(broadcast: IBroadcast<T>): T
• useRunnerStatus<T>(broadcast: IRunnerBroadcast<T>): Status
• useRunnerProgress<T>(broadcast: IRunnerBroadcast<T>): number
• useRunnerError<T>(broadcast: IRunnerBroadcast<T>): Error | null

API Reference

Signal

Methods

• set(value: T): void
• transform(cb: (val: T) => T): void
• subscribe(callback: (value: T) => void): ISubscription
• dispose(): void

Runner

Methods

• execute(action: () => Promise<T>): Promise
• dispatch(action: () => Promise<T>): Promise
• retry(): Promise
• reset(): void
• setProgress(progress: number): void
• setFeedback(feedback: string): void
• setError(error: Error | null): void
• dispose(): void

Troubleshooting

• Memory Management

  • Its advised to call dispose() on signals and runners when they're no longer needed, but not necessary because Signals subscriptions are WeakRefs
  • When using the Root Presenter Pattern (injecting presenters through props), DO NOT dispose the presenter in the component
  • When using the Local State Pattern (creating presenters with useState), you MUST dispose the presenter in the component's cleanup function

• Performance

  • Use transform for memory-efficient updates
  • Avoid creating new arrays/objects when updating state
  • Don't create new signals in render methods

• Type Safety

  • Always specify generic types for signals and runners
  • Use TypeScript's type inference when possible
  • Maintain type consistency across your application

Examples

Real-time Data Updates

import { Signal, Runner } from '@tcn/state';

class StockPricePresenter {
  private _priceSignal: Signal<number>;
  private _updateRunner: Runner<void>;
  private _ws: WebSocket | null;
  private _symbol: string;

  get priceBroadcast() {
    return this._priceSignal.broadcast;
  }

  get updateRunnerBroadcast() {
    return this._updateRunner.broadcast;
  }

  constructor(symbol: string) {
    this._symbol = symbol;
    this._priceSignal = new Signal<number>(0);
    this._updateRunner = new Runner<void>();
    this._ws = null;
  }

  async initialize() {
    try {
      this._ws = new WebSocket(`wss://api.example.com/stock/${this._symbol}`);
      
      // Handle WebSocket connection
      this._ws.onopen = () => {
        console.log('WebSocket connected');
      };

      // Handle WebSocket messages
      this._ws.onmessage = (event) => {
        const price = JSON.parse(event.data).price;
        this._priceSignal.set(price);
      };

      // Handle WebSocket errors
      this._ws.onerror = (error) => {
        console.error('WebSocket error:', error);
        this._updateRunner.setError(new Error('WebSocket connection failed'));
      };

      // Handle WebSocket closure
      this._ws.onclose = () => {
        console.log('WebSocket disconnected');
      };

      return true;
    } catch (error) {
      console.error('Failed to initialize WebSocket:', error);
      this._updateRunner.setError(new Error('Failed to initialize WebSocket connection'));
      return false;
    }
  }

  async refresh() {
    await this._updateRunner.dispatch(async () => {
      const response = await fetch(`/api/stock/${this._symbol}`);
      const data = await response.json();
      this._priceSignal.set(data.price);
    });
  }

  dispose() {
    this._ws?.close();
    this._priceSignal.dispose();
    this._updateRunner.dispose();
  }
}

// Usage in React component
function StockPriceView({ presenter }: { presenter: StockPricePresenter }) {
  const price = useSignalValue(presenter.priceBroadcast);
  const status = useRunnerStatus(presenter.updateRunnerBroadcast);
  const error = useRunnerError(presenter.updateRunnerBroadcast);

  useEffect(() => {
    // Initialize WebSocket connection when component mounts
    presenter.initialize();

    // Cleanup when component unmounts
    return () => {
      presenter.dispose();
    };
  }, []);

  if (status === 'ERROR') {
    return (
      <div>
        <p>Error: {error?.message}</p>
        <button onClick={() => presenter.initialize()}>Retry Connection</button>
      </div>
    );
  }

  return (
    <div>
      <h2>Stock Price: ${price}</h2>
      <button onClick={() => presenter.refresh()}>Refresh Price</button>
    </div>
  );
}

Presenter Composition

// AppPresenter.ts
class AppPresenter {
  // Pattern 1: Readonly property for permanent presenters
  // - Used when the child presenter is always needed
  // - The child presenter is created once and lives as long as the parent
  // - Access is direct and type-safe
  readonly toolbarPresenter: ToolbarPresenter;

  // Pattern 2: Signal for dynamic presenters
  // - Used when the child presenter may come and go
  // - The child presenter can be created and disposed on demand
  // - Access requires checking for null
  private _sidebarSignal: Signal<SidebarPresenter | null>;

  get sidebarBroadcast() {
    return this._sidebarSignal.broadcast;
  }

  constructor() {
    // Pattern 1: Initialize permanent presenters in constructor
    this.toolbarPresenter = new ToolbarPresenter();
    
    // Pattern 2: Initialize signal with null for dynamic presenters
    this._sidebarSignal = new Signal<SidebarPresenter | null>(null);
  }

  toggleSidebar() {
    if (this._sidebarSignal.get() === null) {
      // Pattern 2: Create new presenter when needed
      this._sidebarSignal.set(new SidebarPresenter());
    } else {
      // Pattern 2: Clean up and remove presenter when no longer needed
      this._sidebarSignal.get()?.dispose();
      this._sidebarSignal.set(null);
    }
  }

  dispose() {
    // Pattern 1: Clean up permanent presenters
    this.toolbarPresenter.dispose();
    
    // Pattern 2: Clean up dynamic presenters if they exist
    this._sidebarSignal.get()?.dispose();
    this._sidebarSignal.dispose();
  }
}

// App.tsx
function App() {
  const [appPresenter] = useState(() => new AppPresenter());
  const sidebarPresenter = useSignalValue(appPresenter.sidebarBroadcast);

  useEffect(() => {
    return () => appPresenter.dispose();
  }, [appPresenter]);

  return (
    <div className="app">
      {/* Pattern 1: Direct access to permanent presenter */}
      <Toolbar presenter={appPresenter.toolbarPresenter} />
      
      <div className="content">
        <button onClick={() => appPresenter.toggleSidebar()}>
          {sidebarPresenter ? 'Hide Sidebar' : 'Show Sidebar'}
        </button>
        
        {/* Pattern 2: Conditional rendering based on presenter existence */}
        {sidebarPresenter && (
          <Sidebar presenter={sidebarPresenter} />
        )}
      </div>
    </div>
  );
}

Presenter Composition Patterns

The library supports two main patterns for composing presenters:

1. Permanent Presenters (Readonly Properties)

class ParentPresenter {
  // Child presenter is always available
  readonly childPresenter: ChildPresenter;
  
  constructor() {
    this.childPresenter = new ChildPresenter();
  }
}

Use this pattern when:

• The child presenter is always needed
• The child's lifecycle matches the parent's
• You need direct, type-safe access to the child

2. Dynamic Presenters (Signals)

class ParentPresenter {
  private _childSignal: Signal<ChildPresenter | null>;
  
  get childBroadcast() {
    return this._childSignal.broadcast;
  }
  
  constructor() {
    this._childSignal = new Signal<ChildPresenter | null>(null);
  }
  
  toggleChild() {
    if (this._childSignal.get() === null) {
      this._childSignal.set(new ChildPresenter());
    } else {
      this._childSignal.get()?.dispose();
      this._childSignal.set(null);
    }
  }
}

Use this pattern when:

• The child presenter may come and go
• The child's lifecycle is independent of the parent
• You need to conditionally render components based on the child's existence

Choosing Between Patterns

• Use Permanent Presenters when:

  • The child is a core part of the parent's functionality
  • The child's state needs to persist as long as the parent exists
  • You need direct access to the child's methods and properties

• Use Dynamic Presenters when:

  • The child is optional or can be toggled
  • The child's state can be discarded when not needed
  • You want to save memory by disposing of unused presenters
  • The child's existence affects the UI layout

Best Practices

• Memory Management:

  • Always dispose of presenters when they're no longer needed
  • For permanent presenters, dispose them in the parent's dispose method
  • For dynamic presenters, dispose them before setting the signal to null

• Type Safety:

  • Use TypeScript's type system to ensure proper access to presenters
  • For dynamic presenters, always check for null before accessing

• Component Integration:

  • Use useSignalValue to subscribe to dynamic presenter signals
  • Pass permanent presenters directly as props
  • Use conditional rendering for dynamic presenters