Github Spark Bug: useKV hook throws TypeError on undefined prevDeps during component lifecycle

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Summary

The useKV hook from the @github/spark/hooks package can cause a hard crash in a React application. During the component render lifecycle, it attempts to access the length property of a variable named prevDeps, which is sometimes undefined. This results in an unhandled TypeError: can't access property "length", prevDeps is undefined.

This issue makes the useKV hook unreliable in certain component lifecycle scenarios (e.g., re-renders or unmounting) and forces a fallback to alternative state management.

Steps to Reproduce

1. Integrate @github/spark/hooks into a standard React 19 + Vite application.
2. Use the useKV hook within a component to manage a piece of state.
3. Trigger a re-render of the component.
4. The application crashes, and the following error appears in the browser console.

Error and Stack Trace

TypeError: can't access property "length", prevDeps is undefined
    React 3
    useKV index.js:26
    useKeyValue App.tsx:5
    App App.tsx:232
    React 8
    performWorkUntilDeadline scheduler.production.js:143

The key part of the stack trace points directly to an internal error within the useKV implementation.

Expected Behavior

The useKV hook should handle its internal dependency arrays safely and should not crash if prevDeps is undefined at any point during the React render cycle. It should be resilient to standard component re-renders.

Actual Behavior

The hook throws an unhandled TypeError, crashing the entire React application.

Environment

• React: 19.0.0
• Vite: 6.3.5
• @github/spark: ^0.39.0

Workaround Implemented

As a temporary fix, we have wrapped the call to useKV in a try...catch block to prevent the application from crashing. If an error is caught, we fall back to using a useLocalStorage hook instead.

// Example of the workaround
let _kvImpl = mod.useKV;

export function useKeyValue(key, defaultValue) {
  if (_kvImpl) {
    try {
      // Attempt to use the spark hook
      return _kvImpl(key, defaultValue);
    } catch (err) {
      console.warn('Spark useKV failed, falling back to localStorage.', err);
      // On failure, disable it for the session and fall back
      _kvImpl = null;
    }
  }
  return useLocalStorage(key, defaultValue);
}

This workaround ensures the application remains stable, but it highlights a potential robustness issue within the hook itself.

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