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?
Try like below
const [active, setActive] = useState(props.isFilterMode ? null : 0);
Or
using a callback function (lazy initialisation)
const [active, setActive] = useState(() => props.isFilterMode ? null : 0);
const Component = ({ isFilterMode }) => {
const [active, setActive] = useState(() => isFilterMode ? null : 0);
...
}
you can define an expression with a return value as an argument for useState.
With a ternary operator like 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);
And like Amila suggested in the other answer you can use a callback as a parameter to useState and whatever is evaluated and returned from that callback would be your initial state using arrow functions you would do something like:
const [active, setActive] = useState(() => props.isFilterMode ? null : 0);
or more explicitly but with longer code:
const [active, setActive] = useState(() => { if(props.isFilterMode){ return null;} else { return 0;} } );