---

name: blac-development description: Develop with BlaC state management library for React. Use when creating Cubits, Vertices, using useBloc/useBlocActions hooks, managing state containers, or implementing inter-bloc communication patterns.

BlaC Development Skill

BlaC is a TypeScript state management library with React integration using proxy-based dependency tracking for optimal re-renders.

Installation

Copypnpm add @blac/core @blac/react

Core Concepts

Cubit - Simple State Container

Use Cubit for direct state mutations without events. Best for most use cases.

Copyimport { Cubit } from '@blac/core';

class CounterCubit extends Cubit<{ count: number }> {
  constructor() {
    super({ count: 0 }); // initial state (must be an object)
  }

  // IMPORTANT: Always use arrow functions for React compatibility
  increment = () => {
    this.emit({ count: this.state.count + 1 });
  };

  decrement = () => {
    this.emit({ count: this.state.count - 1 });
  };
}

State Update Methods:

• emit(newState) - Emit new state directly
• update(fn) - Update with function (current) => next
• patch(partial) - Shallow merge partial state (object state only)

Vertex - Event-Driven State Container

Use Vertex for event-driven architectures with explicit state transitions.

Copyimport { Vertex } from '@blac/core';

// Define events as discriminated union
type CounterEvent =
  | { type: 'increment'; amount: number }
  | { type: 'decrement' };

class CounterVertex extends Vertex<{ count: number }, CounterEvent> {
  constructor() {
    super({ count: 0 });

    // TypeScript enforces exhaustive handling - all event types must be handled
    this.createHandlers({
      increment: (event, emit) => {
        emit({ count: this.state.count + event.amount });
      },
      decrement: (_, emit) => {
        emit({ count: this.state.count - 1 });
      },
    });
  }

  // Convenience methods
  increment = (amount = 1) => this.add({ type: 'increment', amount });
  decrement = () => this.add({ type: 'decrement' });
}

Class Configuration with @blac() Decorator

Copyimport { blac, Cubit } from '@blac/core';

// Isolated: Each component gets its own instance
@blac({ isolated: true })
class FormBloc extends Cubit<FormState> {}

// KeepAlive: Never auto-dispose when ref count reaches 0
@blac({ keepAlive: true })
class AuthBloc extends Cubit<AuthState> {}

// Exclude from DevTools (prevents infinite loops)
@blac({ excludeFromDevTools: true })
class InternalBloc extends Cubit<State> {}

// Function syntax (no decorator support)
const MyBloc = blac({ isolated: true })(class extends Cubit<State> {});

Note: BlacOptions is a union type - only ONE option can be specified at a time.

React Integration

useBloc Hook - Automatic Dependency Tracking

Copyimport { useBloc } from '@blac/react';

function Counter() {
  const [state, cubit] = useBloc(CounterCubit);

  // Only re-renders when accessed properties change
  return (
    <div>
      <p>Count: {state.count}</p>
      <button onClick={cubit.increment}>+</button>
    </div>
  );
}

Returns: [state, blocInstance, componentRef]

useBloc Options

Copyconst [state, bloc] = useBloc(MyBloc, {
  props: { userId: '123' },           // Constructor arguments
  instanceId: 'main',                  // Custom instance ID for shared blocs
  dependencies: (state, bloc) => [state.count], // Manual dependency tracking
  autoTrack: false,                    // Disable automatic tracking
  disableGetterCache: false,           // Disable getter value caching (advanced)
  onMount: (bloc) => bloc.fetchData(), // Lifecycle callbacks
  onUnmount: (bloc) => bloc.cleanup(),
});

useBlocActions Hook - Actions Only (No State Subscription)

Copyimport { useBlocActions } from '@blac/react';

function ActionsOnly() {
  const bloc = useBlocActions(CounterBloc);

  // Never re-renders due to state changes
  return <button onClick={bloc.increment}>+</button>;
}

Instance Management

Static Methods

Bloc-to-Bloc Communication

In event handlers or methods (borrowing):

Copyclass UserBloc extends Cubit<UserState> {
  loadProfile = () => {
    // Borrow - no memory leak, no cleanup needed
    const analytics = AnalyticsCubit.get();
    analytics.trackEvent('profile_loaded');
  };
}

In getters (automatic tracking):

Copyclass CartCubit extends Cubit<CartState> {
  get totalWithShipping(): number {
    const shipping = ShippingCubit.get(); // Auto-tracked!
    return this.itemTotal + shipping.state.cost;
  }
}

System Events

Copyclass MyBloc extends Cubit<State> {
  constructor() {
    super(initialState);

    this.onSystemEvent('stateChanged', ({ state, previousState }) => {
      console.log('State changed');
    });

    this.onSystemEvent('propsUpdated', ({ props, previousProps }) => {
      console.log('Props updated');
    });

    this.onSystemEvent('dispose', () => {
      console.log('Disposing - cleanup here');
    });
  }
}

Best Practices

DO:

• Use arrow functions for methods (correct this binding in React)
• Keep state immutable (create new objects/arrays)
• Use patch() for simple field updates, update() for nested changes
• Use useBlocActions when only calling methods (no state reading)
• Use getters for computed values (cached per render cycle)
• Use .get() instead of .resolve() in bloc-to-bloc communication

DON'T:

• Mutate state directly (this.state.todos.push(...))
• Destructure entire state when you only need specific properties
• Use .resolve() in getters (causes memory leaks)
• Use patch() for nested object updates (shallow merge only)

Common Patterns

Form State (Isolated)

Copy@blac({ isolated: true })
class FormBloc extends Cubit<FormState> {
  constructor() {
    super({ values: {}, errors: {}, isSubmitting: false });
  }

  setField = (field: string, value: string) => {
    this.update(state => ({
      ...state,
      values: { ...state.values, [field]: value },
      errors: { ...state.errors, [field]: '' }
    }));
  };
}

Async Data Fetching

Copyclass UserBloc extends Cubit<DataState<User>> {
  constructor() {
    super({ data: null, isLoading: false, error: null });
  }

  fetchUser = async (id: string) => {
    this.patch({ isLoading: true, error: null });
    try {
      const data = await api.getUser(id);
      this.patch({ data, isLoading: false });
    } catch (error) {
      this.patch({ error: error.message, isLoading: false });
    }
  };
}

Shared Singleton Service

Copy@blac({ keepAlive: true })
class AnalyticsService extends Cubit<AnalyticsState> {
  trackEvent = (name: string, data: Record<string, any>) => {
    // Other blocs can safely call: AnalyticsService.get().trackEvent(...)
  };
}

Troubleshooting

Component not re-rendering?

• Access state properties during render, not before
• Check you're using useBloc, not just reading bloc.state

Too many re-renders?

• Access only the properties you need
• Don't destructure entire state object
• Consider useBlocActions for action-only components

Shared state not working?

• Check if bloc is marked @blac({ isolated: true })
• Verify same instanceId if using custom IDs

Performance Optimization

Optimal Property Access

Copy// ✅ OPTIMAL: Access only what you render
function UserCard() {
  const [user] = useBloc(UserBloc);
  return <h2>{user.name}</h2>; // Only tracks 'name'
}

// ❌ AVOID: Destructuring tracks everything
const { name, email, bio } = user; // Re-renders on ANY change

Component Splitting

Copy// ✅ Split into granular components
function TodoApp() {
  return (
    <>
      <TodoCount />    {/* Only re-renders on count change */}
      <TodoList />     {/* Only re-renders on todos change */}
      <TodoActions />  {/* Never re-renders (uses useBlocActions) */}
    </>
  );
}

function TodoActions() {
  const cubit = useBlocActions(TodoCubit); // No state subscription
  return <button onClick={cubit.addTodo}>Add</button>;
}

Performance Summary

Common Mistakes

1. Destructuring state - Tracks all destructured properties
2. Spreading props - <Child {...state} /> defeats tracking
3. Using .resolve() in methods - Use .get() for bloc-to-bloc calls
4. Not using useBlocActions - Creates unnecessary subscriptions

For complete API reference, see REFERENCE.md.