Updating state on props change in React Form

Question

I am having trouble with a React form and managing the state properly. I have a time input field in a form (in a modal). The initial value is set as a state variable in

Answer 1

Use Memoize

The op's derivation of state is a direct manipulation of props, with no true derivation needed. In other words, if you have a prop which can be utilized or transformed directly there is no need to store the prop on state.

Given that the state value of start_time is simply the prop start_time.format("HH:mm"), the information contained in the prop is already in itself sufficient for updating the component.

However if you did want to only call format on a prop change, the correct way to do this per latest documentation would be via Memoize: https://reactjs.org/blog/2018/06/07/you-probably-dont-need-derived-state.html#what-about-memoization