use-state-reducer

A versatile React hook that bridges the gap between Uncontrolled State, Controlled State, and the State Reducer Pattern.
It allows components to manage their own state while giving parents the power to intercept, modify, or even cancel state updates.

📦 Installation

npm install use-state-reducer

✨ Features

• Uncontrolled by Default: Works like a standard useState if no external value is provided.
• Fully Controllable: Syncs perfectly with external props when a value is passed.
• State Interception: Use externalUpdater to implement validation, logging, or custom transformation logic before the state actually changes.

---

🚀 Usage Examples

1. Uncontrolled Mode (Basic)

Use it just like useState. The component manages its own state.

const [state, setState] = useStateReducer(0);
// state is managed internally

2. Controlled Mode (Sync with Parent)

When a value prop is passed, the hook follows the parent's state.

function Parent() {
  const [val, setVal] = useState("Hello");
  return <Child value={val} onValueChange={setVal} />;
}

function Child({ value, onValueChange }) {
  const [state, setState] = useStateReducer("", value, (prev, next) => {
    onValueChange(next); // Sync back to parent
    return next;
  });

  return <input value={state} onChange={(e) => setState(e.target.value)} />;
}

3. Interception Mode (The "Interrupt" Pattern)

This is where this hook shines. Even in Uncontrolled mode, the parent can "intercept" the update to apply logic, like a State Reducer.

function LimitedCounter() {
  const [state, setState] = useStateReducer(
    0,
    undefined, // Keep it uncontrolled
    (prev, next) => {
      // 🛡️ Interception Logic: Max value is 10
      if (next > 10) {
        alert("Cannot exceed 10!");
        return prev; // Return previous state to "cancel" the update
      }

      console.log(`Changing from ${prev} to ${next}`);
      return next; // Apply the update
    },
  );

  return <button onClick={() => setState(state + 1)}>{state}</button>;
}

---

📚 API Reference

const [state, setState] = useStateReducer(initValue, value, externalUpdater?);

Parameters

Parameter	Type	Description
initValue	T	The initial state (used in Uncontrolled mode).
value	T | undefined	The external state. If not undefined, the hook enters Controlled mode.
externalUpdater	(prev, next) => T | undefined	(Optional) A function that intercepts the update. Returns the next state to apply, or undefined to skip the update.

Returns

• [state, setState]:
  • state: The current active state (internal if uncontrolled, external if controlled).
  • setState: A function to trigger a state update. It automatically handles the externalUpdater logic and checks for control status.

---

💡 Why use this over useControllableState?

Standard controllable hooks usually only switch between internal/external state. useStateReducer adds a Middleware Layer (externalUpdater).

This allows you to:

1. Validate state changes before they happen.
2. Transform data (e.g., forcing uppercase on an input).
3. Trigger Side Effects (like logging or analytics) exactly when the state is requested to change, without worrying about React's render-cycle purity issues.

📄 License

MIT