Does the setter function for the useState hook overwrite state unexpectedly

Question

With the help of code can you tell me Does the setter function for the useState hook overwrite state unexpectedly?

Answer 1

Yes, the setter function for the useState hook replaces the state instead of merging it. This behavior can lead to unexpected overwrites, especially when managing objects or arrays as state.

Example of Unexpected Overwrite:

const [state, setState] = React.useState({ count: 0, text: '' });

// Updates count but overwrites the state

setState({ count: 1 });

console.log(state); // { count: 1 } -> 'text' is lost!

Why Does This Happen?

Unlike class components, where setState merges updates, the useState setter replaces the state entirely.

Correct Approach:

Preserve previous state using a functional update:

setState(prevState => ({

  ...prevState, // Copy previous state

  count: 1 // Update only count

}));