如何根据 props 在 React 中设置初始 useState 值

Question

I currently set my active state to 0:

const [active, setActive] = useState(0);

but I'm wondering how I can set the initial value to null if one of my component props: isFilterMode is true? So the initial state is "dynamic" based on the props?

Answer 1

Try like this

const [active, setActive] = useState(props.isFilterMode ? null : 0);

or using a callback function ( lazy initialization )

const [active, setActive] = useState(() => props.isFilterMode ? null : 0);

Answer 2

const Component = ({ isFilterMode }) => {
  const [active, setActive] = useState(() => isFilterMode ? null : 0);
  ...
}

Answer 3

you can define an expression with a return value as an argument for useState. With a ternary operator like props.isFilterMode? null: 0 props.isFilterMode? null: 0 you would return null if the value of props.isFilterMode evaluates to true and 0 otherwise. So in useState you would have:

  const [active, setActive] = useState(props.isFilterMode ? null : 0);