Why is a callback used when calling the state change function from useState?

Question

React

const [value, setValue] = useState(null)
//...
function handler(newValue) {
  setValue(() => newValue)
}

Answer 1

Here is the answer

Answer 2

In your example, it makes no sense.
And so it is usually used to set the state based on the previous value of the state

function handler(newValue) {
  setValue((prevState) => prevState + 1) // Установит стейт на основании предыдущего значения + 1
}